http://www.rssboard.org/rss-specification 720 https://escholarship.org/uc/nobel_2020_ghez/rss Recent eScholarship items from Andrea Ghez, UCLA (Nobel Prize in Physics, 2020) Sun, 20 Sep 2026 20:15:41 +0000 https://escholarship.org/uc/item/9w82q28d Context. The Galactic Center black hole and the nuclear star cluster are surrounded by a clumpy ring of gas and dust, the circumnuclear disk (CND), that rotates about them at a standoff distance of ≃1.5 pc. The mass and density of individual clumps in the CND are disputed. Aims. We seek to use H 2 to characterize the clump size distribution and to investigate the morphology and dynamics of the interface between the ionized interior layer of the CND and the molecular reservoir lying farther out (corresponding to the inner rim of the CND, illuminated in ultraviolet light by the central star cluster). Methods. We have observed two fields of approximately 20″ × 20″ in the CND at near-infrared wavelengths with the OSIRIS spectro-imager at the Keck Observatory. These two fields, located at the approaching and receding nodes of the CND, best display this interface. Our data cover two H 2 lines as well as the Br γ line (tracing H II). We have developed the tool CubeFit, an original... https://escholarship.org/uc/item/9w82q28d Wed, 10 Apr 2024 00:00:00 +0000 Paumard, Thibaut Ciurlo, Anna https://orcid.org/0000-0001-5800-3093 Morris, Mark R https://orcid.org/0000-0002-6753-2066 Do, Tuan https://orcid.org/0000-0001-9554-6062 Ghez, Andrea M https://escholarship.org/uc/item/3f98c25f Images obtained with single-conjugate adaptive optics (AO) show spatial variation of the point spread function (PSF) due to both atmospheric anisoplanatism and instrumental aberrations. The poor knowledge of the PSF across the field of view strongly impacts the ability to take full advantage of AO capabilities. The AIROPA project aims to model these PSF variations for the NIRC2 imager at the Keck Observatory. Here, we present the characterization of the instrumental phase aberrations over the entire NIRC2 field of view and we present a metric for quantifying the quality of the calibration, the fraction of variance unexplained (FVU). We used phase diversity measurements obtained on an artificial light source to characterize the variation of the aberrations across the field of view and their evolution with time. We find that there is a daily variation of the wavefront error (RMS of the residuals is 94 nm) common to the whole detector, but the differential aberrations across the... https://escholarship.org/uc/item/3f98c25f Wed, 30 Nov 2022 00:00:00 +0000 Ciurlo, Anna https://orcid.org/0000-0001-5800-3093 Turri, Paolo Witzel, Gunther Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Do, Tuan https://orcid.org/0000-0001-9554-6062 Sitarski, Breann N Fitzgerald, Michael P https://orcid.org/0000-0002-0176-8973 Ghez, Andrea M Alvarez, Carlos Terry, Sean K https://orcid.org/0000-0002-5029-3257 Doppmann, Greg Lyke, James E Ragland, Sam Campbell, Randall Matthews, Keith https://escholarship.org/uc/item/36g080xn IRIS (InfraRed Imaging Spectrograph) is a first light near-infrared diffraction limited imager and integral field spectrograph being designed for the future Thirty Meter Telescope (TMT). IRIS is optimized to perform astronomical studies across a significant fraction of cosmic time, from our Solar System to distant newly formed galaxies (Barton et al. [1]). We present a selection of the innovative science cases that are unique to IRIS in the era of upcoming space and ground-based telescopes. We focus on integral field spectroscopy of directly imaged exoplanet atmospheres, probing fundamental physics in the Galactic Center, measuring 104 to 1010 M supermassive black hole masses, resolved spectroscopy of young star-forming galaxies (1 < 5) and first light galaxies (6 < 12), and resolved spectroscopy of strong gravitational lensed sources to measure dark matter substructure. For each of these science cases we use the IRIS simulator (Wright et al. [2], Do et al. [3]) to explore... https://escholarship.org/uc/item/36g080xn Sat, 9 Apr 2022 00:00:00 +0000 Wright, Shelley A Larkin, James E Moore, Anna M Do, Tuan https://orcid.org/0000-0001-9554-6062 Simard, Luc Adamkovics, Maté Armus, Lee Barth, Aaron J https://orcid.org/0000-0002-3026-0562 Barton, Elizabeth Boyce, Hope Cooke, Jeffrey Cote, Patrick Davidge, Timothy Ellerbroek, Brent Ghez, Andrea M Liu, Michael C Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Macintosh, Bruce A Mao, Shude Marois, Christian Schoeck, Matthias Suzuki, Ryuji Tan, Jonathan C Treu, Tommaso https://orcid.org/0000-0002-8460-0390 Wang, Lianqi Weiss, Jason https://escholarship.org/uc/item/9zm799jv We present improved relative astrometry for stars within the central half parsec of our Galactic Center (GC) based on data obtained with the 10 m W. M. Keck Observatory from 1995 to 2017. The new methods used to improve the astrometric precision and accuracy include correcting for local astrometric distortions, applying a magnitude-dependent additive error, and more carefully removing instances of stellar confusion. Additionally, we adopt jackknife methods to calculate velocity and acceleration uncertainties. The resulting median proper motion uncertainty is 0.05 mas yr−1 for our complete sample of 1184 stars in the central 10″ (0.4 pc). We have detected 24 accelerating sources, 2.6 times more than the number of previously published accelerating sources, which extend out to 4″ (0.16 pc) from the black hole. Based on S0-2's orbit, our new astrometric analysis has reduced the systematic error of the supermassive black hole (SMBH) by a factor of 2. The linear drift in our astrometric... https://escholarship.org/uc/item/9zm799jv Thu, 8 Oct 2020 00:00:00 +0000 Jia, Siyao Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Sakai, S Gautam, AK Do, T https://orcid.org/0000-0001-9554-6062 Hosek, MW https://orcid.org/0000-0003-2874-1196 Service, M Ghez, AM Gallego-Cano, E Schödel, R Hees, Aurelien Morris, MR https://orcid.org/0000-0002-6753-2066 Becklin, E Matthews, K https://escholarship.org/uc/item/8s67j8n7 The star S0-2, which orbits the supermassive black hole (SMBH) in our Galaxy with a period of 16 years, provides the strongest constraint on both the mass of the SMBH and the distance to the Galactic center. S0-2 will soon provide the first measurement of relativistic effects near a SMBH. We report the first limits on the binarity of S0-2 from radial velocity (RV) monitoring, which has implications for both understanding its origin and robustness as a probe of the central gravitational field. With 87 RV measurements, which include 12 new observations that we present, we have the requisite data set to look for RV variations from S0-2's orbital model. Using a LombScargle analysis and orbit-fitting for potential binaries, we detect no RV variation beyond S0-2's orbital motion and do not find any significant periodic signal. The lack of a binary companion does not currently distinguish different formation scenarios for S0-2. The upper limit on the mass of a companion star (Mcomp)... https://escholarship.org/uc/item/8s67j8n7 Thu, 8 Oct 2020 00:00:00 +0000 Chu, Devin S Do, Tuan https://orcid.org/0000-0001-9554-6062 Hees, Aurelien Ghez, Andrea Naoz, Smadar Witzel, Gunther Sakai, Shoko Chappell, Samantha Gautam, Abhimat K Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Matthews, Keith https://escholarship.org/uc/item/8qd686h8 We used 4-yr baseline Hubble Space Telescope/Wide Field Camera 3 IR observations of the Galactic Centre in the F153M band (1.53 μm) to identify variable stars in the central ~2.3 arcmin × 2.3 arcmin field.We classified 3845 long-term (periods from months to years) and 76 short-term (periods of a few days or less) variables among a total sample of 33 070 stars. For 36 of the latter ones, we also derived their periods (< 3 d). Our catalogue not only confirms bright long period variables and massive eclipsing binaries identified in previous works but also contains many newly recognized dim variable stars. For example, we found δ Scuti and RR Lyrae stars towards the Galactic Centre for the first time, as well as one BL Her star (period < 1.3 d). We cross-correlated our catalogue with previous spectroscopic studies and found that 319 variables have well-defined stellar types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant branch stars. We used colours... https://escholarship.org/uc/item/8qd686h8 Thu, 8 Oct 2020 00:00:00 +0000 Dong, Hui Schödel, Rainer Williams, Benjamin F Nogueras-Lara, Francisco Gallego-Cano, Eulalia Gallego-Calvente, Teresa Wang, Q Daniel Morris, Mark R https://orcid.org/0000-0002-6753-2066 Do, Tuan Ghez, Andrea https://escholarship.org/uc/item/8262h10z We present an ≈11.5 yr adaptive optics (AO) study of stellar variability and search for eclipsing binaries in the central ∼0.4 pc (∼10″) of the Milky Way nuclear star cluster. We measure the photometry of 563 stars using the Keck II NIRC2 imager (K′-band, λ 0 = 2.124 μm). We achieve a photometric uncertainty floor of Δm K′ ∼ 0.03 (≈3%), comparable to the highest precision achieved in other AO studies. Approximately half of our sample (50% ± 2%) shows variability: 52% ±5% of known early-type young stars and 43% ±4% of known late-type giants are variable. These variability fractions are higher than those of other young, massive star populations or late-type giants in globular clusters, and can be largely explained by two factors. First, our experiment time baseline is sensitive to long-term intrinsic stellar variability. Second, the proper motion of stars behind spatial inhomogeneities in the foreground extinction screen can lead to variability. We recover the two known Galactic... https://escholarship.org/uc/item/8262h10z Thu, 8 Oct 2020 00:00:00 +0000 Gautam, Abhimat Krishna Do, Tuan https://orcid.org/0000-0001-9554-6062 Ghez, Andrea M Morris, Mark R https://orcid.org/0000-0002-6753-2066 Martinez, Gregory D Hosek, Matthew W https://orcid.org/0000-0003-2874-1196 Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Sakai, Shoko Witzel, Gunther Jia, Siyao Becklin, Eric E Matthews, Keith https://escholarship.org/uc/item/7sb2p711 We report new infrared (IR) measurements of the supermassive black hole at the Galactic Center, Sgr A∗, over a decade that was previously inaccessible at these wavelengths. This enables a variability study that addresses variability timescales that are 10 times longer than earlier published studies. Sgr A∗ was initially detected in the near-infrared (NIR) with adaptive optics observations in 2002. While earlier data exists in form of speckle imaging (1995-2005), Sgr A∗ was not detected in the initial analysis. Here, we improved our speckle holography analysis techniques. This has improved the sensitivity of the resulting speckle images by up to a factor of three. Sgr A∗ is now detectable in the majority of epochs covering 7 yr. The brightness of Sgr A∗ in the speckle data has an average observed K magnitude of 16.0, which corresponds to a dereddened flux density of 3.4 mJy. Furthermore, the flat power spectral density of Sgr A∗ between ∼80 days and 7 yr shows its uncorrelation... https://escholarship.org/uc/item/7sb2p711 Thu, 8 Oct 2020 00:00:00 +0000 Chen, Zhuo Gallego-Cano, E Do, T https://orcid.org/0000-0001-9554-6062 Witzel, G Ghez, AM Schödel, R Sitarski, BN Becklin, EE Lu, J https://orcid.org/0000-0001-9611-0009 Morris, MR https://orcid.org/0000-0002-6753-2066 Dehghanfar, A Gautam, AK Hees, A Hosek, MW https://orcid.org/0000-0003-2874-1196 Jia, S Mangian, AC Matthews, K https://escholarship.org/uc/item/7rn1818g Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K ≥ 15) stellar population in the Milky Way's nuclear star cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analysed HST/WFC3/IR observations of the central 2.3 × 2.3 arcmin2 of the Milky Way and found 21 variable stars with periods between 0.2 and 1 d. Here, we present a further comprehensive analysis of these stars. The period- luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as 4 RRc stars, 4 RRab stars, 3 RRab candidates and 10 binaries. Especially, the four RRab stars show sawtooth light curves and fall exactly on to the Oosterhoff I division in the Bailey diagram. Compared to the RRab stars reported by Minniti et al., our new RRab stars have higher extinction (AK > 1.8)... https://escholarship.org/uc/item/7rn1818g Thu, 8 Oct 2020 00:00:00 +0000 Dong, Hui Schödel, Rainer Williams, Benjamin F Nogueras-Lara, Francisco Gallego-Cano, Eulalia Gallego-Calvente, Teresa Wang, Q Daniel Rich, R Michael Morris, Mark R https://orcid.org/0000-0002-6753-2066 Do, Tuan Ghez, Andrea https://escholarship.org/uc/item/7hs3z536 We present the first detection from the Spitzer Space Telescope of 4.5 μm variability from Sgr A∗, the emitting source associated with the Milky Way's central black hole. The >23 hr continuous light curve was obtained with the Infrared Array Camera (IRAC) instrument in 2013 December. The result characterizes the variability of Sgr A∗ prior to the closest approach of the tidally deformed G2 object, a putative infalling gas cloud that orbits close to Sgr A∗. The high stellar density at the location of Sgr A∗ produces a background of ∼250 mJy at 4.5 μm in each pixel with a large pixel-to-pixel gradient, but the light curve for the highly variable Sgr A∗ source was successfully measured by modeling and removing the variations due to pointing wobble. The observed flux densities range from the noise level of ∼ksim;0.7 mJy rms in a 6.4 s measurement to ≳10 mJy. Emission was seen above the noise level ∼ksim;34% of the time. The light-curve characteristics, including the flux density... https://escholarship.org/uc/item/7hs3z536 Thu, 8 Oct 2020 00:00:00 +0000 Hora, JL Witzel, G Ashby, MLN Becklin, EE Carey, S Fazio, GG Ghez, A Ingalls, J Meyer, L Morris, MR https://orcid.org/0000-0002-6753-2066 Smith, HA Willner, SP https://escholarship.org/uc/item/6tc234dz We present adaptive-optics assisted near-infrared high-spectral-resolution observations of late-type giants in the nuclear star cluster of the Milky Way. The metallicity and elemental abundance measurements of these stars offer us an opportunity to understand the formation and evolution of the nuclear star cluster. In addition, their proximity to the supermassive black hole (∼0.5 pc) offers a unique probe of the star formation and chemical enrichment in this extreme environment. We observed two stars identified by medium spectral-resolution observations as potentially having very high metallicities. We use spectral-template fitting with the PHOENIX grid and Bayesian inference to simultaneously constrain the overall metallicity, [M/H], alpha-element abundance [α/Fe], effective temperature, and surface gravity of these stars. We find that one of the stars has very high metallicity ([M/H] > 0.6) and the other is slightly above solar metallicity. Both Galactic center stars have... https://escholarship.org/uc/item/6tc234dz Thu, 8 Oct 2020 00:00:00 +0000 Do, Tuan https://orcid.org/0000-0001-9554-6062 Kerzendorf, Wolfgang Konopacky, Quinn Marcinik, Joseph M Ghez, Andrea Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Morris, Mark R https://orcid.org/0000-0002-6753-2066 https://escholarship.org/uc/item/67q501xs Most, if not all, stars in the field are born in binary configurations or higher multiplicity systems. In dense stellar environment such as the Galactic Center (GC), many stars are expected to be in binary configurations as well. These binaries form hierarchical triple body systems, with the massive black hole (MBH) as the third, distant object. The stellar binaries are expected to undergo large amplitude eccentricity and inclination oscillations via the so-called "eccentric Kozai-Lidov" (EKL) mechanism. These eccentricity excitations, combined with post main sequence stellar evolution, can drive the inner stellar binaries to merge. We study the mergers of stellar binaries in the inner 0.1 pc of the GC caused by gravitational perturbations due to the MBH. We run a large set of Monte Carlo simulations that include the secular evolution of the orbits, general relativistic precession, tides, and post-main-sequence stellar evolution. We find that about 13 % of the initial binary population... https://escholarship.org/uc/item/67q501xs Thu, 8 Oct 2020 00:00:00 +0000 Stephan, Alexander P Naoz, Smadar Ghez, Andrea M Witzel, Gunther Sitarski, Breann N Do, Tuan Kocsis, Bence https://escholarship.org/uc/item/5z53q6qk We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M ∼ 0.01-0.1 M ). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 (ρ = 0.″105/15 AU), 2MASS J04221332+1934392 (ρ = 0.″05/7 AU), and ISO 217 (ρ = 0.″03/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco (τ ∼ 10 Myr), we measure binary fractions of 14/93 = for M4-M6 (M ∼ 0.1-0.3 M ) and 4/108 = for >M6 (M ≲ 0.1 M ) at separations of >10... https://escholarship.org/uc/item/5z53q6qk Thu, 8 Oct 2020 00:00:00 +0000 Todorov, KO Luhman, KL Konopacky, QM McLeod, KK Apai, D Ghez, AM Pascucci, I Robberto, M https://escholarship.org/uc/item/5t60r26s The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared Imaging Spectrograph) will complete its preliminary design phase in 2016. The IRIS instrument design includes a near-infrared (0.85-2.4 micron) integral field spectrograph (IFS) and imager that are able to conduct simultaneous diffraction-limited observations behind the advanced adaptive optics system NFIRAOS. The IRIS science cases have continued to be developed and new science studies have been investigated to aid in technical performance and design requirements. In this development phase, the IRIS science team has paid particular attention to the selection of filters, gratings, sensitivities of the entire system, and science cases that will benefit from the parallel mode of the IFS and imaging camera. We present new science cases for IRIS using the latest end-To-end data simulator on the following topics: Solar System bodies, the Galactic center, active galactic nuclei (AGN), and distant gravitationally-lensed... https://escholarship.org/uc/item/5t60r26s Thu, 8 Oct 2020 00:00:00 +0000 Wright, Shelley A Walth, Gregory Do, Tuan https://orcid.org/0000-0001-9554-6062 Marshall, Daniel Larkin, James E Moore, Anna M Adamkovics, Mate Andersen, David Armus, Lee Barth, Aaron https://orcid.org/0000-0002-3026-0562 Cote, Patrick Cooke, Jeff Davidge, Timothy Dunn, Jennifer S Dumas, Christophe Ellerbroek, Brent L Chisholm, Eric M Ghez, Andrea M Hao, Lei Hayano, Yutaka Liu, Michael Lopez-Rodriguez, Enrique Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Mao, Shude Marois, Christian Pandey, Shashi B Phillips, Andrew C Schoeck, Matthias Subramanian, Annapurni Subramanian, Smitha Suzuki, Ryuji Tan, Jonathan C Terai, Tsuyoshi Treu, Tommaso https://orcid.org/0000-0002-8460-0390 Simard, Luc Weiss, Jason L Wincentsen, James Wong, Michael Zhang, Kai https://escholarship.org/uc/item/58v61996 The population of young stars near the supermassive black hole (SMBH) in the Galactic Center (GC) has presented an unexpected challenge to theories of star formation. Kinematic measurements of these stars have revealed a stellar disk structure (with an apparent 20% disk membership) that has provided important clues regarding the origin of these mysterious young stars. However, many of the apparent disk properties are difficult to explain, including the low disk membership fraction and the high eccentricities given the youth of this population. Thus far, all efforts to derive the properties of this disk have made the simplifying assumption that stars at the GC are single stars. Nevertheless, stellar binaries are prevalent in our Galaxy, and recent investigations suggested that they may also be abundant in the Galactic Center. Here, we show that binaries in the disk can largely alter the apparent orbital properties of the disk. The motion of binary members around each other adds... https://escholarship.org/uc/item/58v61996 Thu, 8 Oct 2020 00:00:00 +0000 Naoz, Smadar Ghez, Andrea M Hees, Aurelien Do, Tuan https://orcid.org/0000-0001-9554-6062 Witzel, Gunther Lu, Jessica R https://orcid.org/0000-0001-9611-0009 https://escholarship.org/uc/item/5721c7f9 We propose a new approach to Bayesian prior probability distributions (priors) that can improve orbital solutions for low-phase-coverage orbits, where data cover less than ∼40% of an orbit. In instances of low phase coverage - such as with stellar orbits in the Galactic center or with directly imaged exoplanets - data have low constraining power and thus priors can bias parameter estimates and produce underestimated confidence intervals. Uniform priors, which are commonly assumed in orbit fitting, are notorious for this. We propose a new observable-based prior paradigm that is based on uniformity in observables. We compare performance of this observable-based prior and of commonly assumed uniform priors using Galactic center and directly imaged exoplanet (HR 8799) data. The observable-based prior can reduce biases in model parameters by a factor of two and helps avoid underestimation of confidence intervals for simulations with less than ∼40% phase coverage. Above this threshold,... https://escholarship.org/uc/item/5721c7f9 Thu, 8 Oct 2020 00:00:00 +0000 O’Neil, K Kosmo Martinez, GD Hees, A Ghez, AM Do, T https://orcid.org/0000-0001-9554-6062 Witzel, G Konopacky, Q Becklin, EE Chu, DS Lu, JR https://orcid.org/0000-0001-9611-0009 Matthews, K Sakai, S https://escholarship.org/uc/item/52m3k72k The general theory of relativity predicts that a star passing close to a supermassive black hole should exhibit a relativistic redshift. In this study, we used observations of the Galactic Center star S0-2 to test this prediction. We combined existing spectroscopic and astrometric measurements from 1995-2017, which cover S0-2's 16-year orbit, with measurements from March to September 2018, which cover three events during S0-2's closest approach to the black hole. We detected a combination of special relativistic and gravitational redshift, quantified using the redshift parameter ϒ. Our result, ϒ = 0.88 ± 0.17, is consistent with general relativity (ϒ = 1) and excludes a Newtonian model (ϒ = 0) with a statistical significance of 5σ. https://escholarship.org/uc/item/52m3k72k Thu, 8 Oct 2020 00:00:00 +0000 Do, Tuan https://orcid.org/0000-0001-9554-6062 Hees, Aurelien Ghez, Andrea Martinez, Gregory D Chu, Devin S Jia, Siyao Sakai, Shoko Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Gautam, Abhimat K O'Neil, Kelly Kosmo https://orcid.org/0000-0003-2400-7322 Becklin, Eric E Morris, Mark R https://orcid.org/0000-0002-6753-2066 Matthews, Keith Nishiyama, Shogo Campbell, Randy Chappell, Samantha Chen, Zhuo Ciurlo, Anna https://orcid.org/0000-0001-5800-3093 Dehghanfar, Arezu Gallego-Cano, Eulalia Kerzendorf, Wolfgang E Lyke, James E Naoz, Smadar Saida, Hiromi Schödel, Rainer Takahashi, Masaaki Takamori, Yohsuke Witzel, Gunther Wizinowich, Peter https://escholarship.org/uc/item/5185m01m Searching for space-time variations of the constants of Nature is a promising way to search for new physics beyond general relativity and the standard model motivated by unification theories and models of dark matter and dark energy. We propose a new way to search for a variation of the fine-structure constant using measurements of late-type evolved giant stars from the S star cluster orbiting the supermassive black hole in our Galactic Center. A measurement of the difference between distinct absorption lines (with different sensitivity to the fine structure constant) from a star leads to a direct estimate of a variation of the fine structure constant between the star's location and Earth. Using spectroscopic measurements of five stars, we obtain a constraint on the relative variation of the fine structure constant below 10^{-5}. This is the first time a varying constant of nature is searched for around a black hole and in a high gravitational potential. This analysis shows new... https://escholarship.org/uc/item/5185m01m Thu, 8 Oct 2020 00:00:00 +0000 Hees, A Do, T https://orcid.org/0000-0001-9554-6062 Roberts, BM Ghez, AM Nishiyama, S Bentley, RO Gautam, AK Jia, S Kara, T Lu, JR https://orcid.org/0000-0001-9611-0009 Saida, H Sakai, S Takahashi, M Takamori, Y https://escholarship.org/uc/item/4mv7r3z5 Continuously time variable sources are often characterized by their power spectral density and flux distribution. These quantities can undergo dramatic changes over time if the underlying physical processes change. However, some changes can be subtle and not distinguishable using standard statistical approaches. Here, we report a methodology that aims to identify distinct but similar states of time variability. We apply this method to the Galactic supermassive black hole, where 2.2 μm flux is observed from a source associated with Sgr A* and where two distinct states have recently been suggested. Our approach is taken from mathematical finance and works with conditional flux density distributions that depend on the previous flux value. The discrete, unobserved (hidden) state variable is modeled as a stochastic process and the transition probabilities are inferred from the flux density time series. Using the most comprehensive data set to date, in which all Keck and a majority... https://escholarship.org/uc/item/4mv7r3z5 Thu, 8 Oct 2020 00:00:00 +0000 Meyer, L Witzel, G Longstaff, FA Ghez, AM https://escholarship.org/uc/item/4cr04225 We present new observations and analysis of G2 - the intriguing red emission-line object which is quickly approaching the Galaxy's central black hole. The observations were obtained with the laser guide star adaptive optics systems on the W. M. Keck I and II telescopes (2006-2012) and include spectroscopy (R ∼ 3600) centered on the hydrogen Brγ line as well as K' (2.1 μm) and L' (3.8 μm) imaging. Analysis of these observations shows the Brγ line emission has a positional offset from the L' continuum. This offset is likely due to background source confusion at L'. We therefore present the first orbital solution derived from Brγ line astrometry, which, when coupled with radial velocity measurements, results in a later time of closest approach (2014.21 ± 0.14), closer periastron (130 AU, 1600 R s), and higher eccentricity (0.9814 ± 0.0060) compared to a solution using L' astrometry. It is shown that G2 has no K' counterpart down to K' ∼ 20 mag. G2's L' continuum and the Brγ line... https://escholarship.org/uc/item/4cr04225 Thu, 8 Oct 2020 00:00:00 +0000 Phifer, K Do, T Meyer, L Ghez, AM Witzel, G Yelda, S Boehle, A Lu, JR https://orcid.org/0000-0001-9611-0009 Morris, MR https://orcid.org/0000-0002-6753-2066 Becklin, EE Matthews, K https://escholarship.org/uc/item/37v451vk We present new, more precise measurements of the mass and distance of our Galaxy's central supermassive black hole, Sgr A∗. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A∗, combining 2 decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star's orbit from the deep adaptive optics data (2005-2013) to inform the search for the star in the speckle years (1995-2005). When this new analysis technique is combined with the first complete re-reduction of Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 (K-band magnitude = 17, orbital period = 19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass (M bh) and distance... https://escholarship.org/uc/item/37v451vk Thu, 8 Oct 2020 00:00:00 +0000 Boehle, A Ghez, AM Schödel, R Meyer, L Yelda, S Albers, S Martinez, GD Becklin, EE Do, T Lu, JR https://orcid.org/0000-0001-9611-0009 Matthews, K Morris, MR https://orcid.org/0000-0002-6753-2066 Sitarski, B Witzel, G https://escholarship.org/uc/item/36m6393z As a young massive cluster in the central molecular zone, the Arches cluster is a valuable probe of the stellar initial mass function (IMF) in the extreme Galactic center environment. We use multi-epoch Hubble Space Telescope observations to obtain high-precision proper-motion and photometric measurements of the cluster, calculating cluster membership probabilities for stars down to ∼1.8 M⊙ between cluster radii of 0.25 and 3.0 pc. We achieve a cluster sample with just ∼6% field contamination, a significant improvement over photometrically selected samples that are severely compromised by the differential extinction across the field. Combining this sample with K-band spectroscopy of five cluster members, we forward model the Arches cluster to simultaneously constrain its IMF and other properties (such as age and total mass) while accounting for observational uncertainties, completeness, mass segregation, and stellar multiplicity. We find that the Arches IMF is best described by... https://escholarship.org/uc/item/36m6393z Thu, 8 Oct 2020 00:00:00 +0000 Hosek, Matthew W https://orcid.org/0000-0003-2874-1196 Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Anderson, Jay Najarro, Francisco Ghez, Andrea M Morris, Mark R https://orcid.org/0000-0002-6753-2066 Clarkson, William I Albers, Saundra M https://escholarship.org/uc/item/32d3s7hm Context. Our general understanding of multiple star and planet formation is primarily based on observations of young multiple systems in low density regions like Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters, observational constraints from young binaries in those environments are fundamental for understanding both the formation of multiple systems and planets in multiple systems throughout the Galaxy. Aims. We build upon the largest survey for young binaries in the Orion Nebula Cluster (ONC), which is based on Hubble Space Telescope observations to derive both stellar and circumstellar properties of newborn binary systems in this cluster environment. Methods. We present adaptive optics spatially-resolved JHKL′-band photometry and K-band R ~ 5000 spectra for a sample of eight ONC binary systems from this database. We characterize the stellar properties of binary components and obtain a census of protoplanetary disks through K - L′ color excess. For... https://escholarship.org/uc/item/32d3s7hm Thu, 8 Oct 2020 00:00:00 +0000 Correia, S Duchêne, G Reipurth, B Zinnecker, H Daemgen, S Petr-Gotzens, MG Köhler, R Ratzka, Th Aspin, C Konopacky, QM Ghez, AM https://escholarship.org/uc/item/27n7t5mq In various fields of physics and astronomy, access to experimental facilities or to telescopes is becoming more and more competitive and limited. It therefore becomes important to optimize the type of measurements and their scheduling to reach a given scientific objective and to increase the chances of success of a scientific project. In this communication, extending the work of Ford and of Loredo et al., we present an efficient adaptive scheduling tool aimed at prioritizing measurements in order to reach a scientific goal. The algorithm, based on the Fisher matrix, can be applied to a wide class of measurements. We present this algorithm in detail and discuss some practicalities such as systematic errors or measurement losses due to contingencies (such as weather, experimental failure, ...). As an illustration, we consider measurements of the short-period star S0-2 in our Galactic Center (GC). We show that the radial velocity measurements at the two turning points of the radial... https://escholarship.org/uc/item/27n7t5mq Thu, 8 Oct 2020 00:00:00 +0000 Hees, A Dehghanfar, A Do, T https://orcid.org/0000-0001-9554-6062 Ghez, AM Martinez, GD Campbell, R Lu, JR https://orcid.org/0000-0001-9611-0009 https://escholarship.org/uc/item/2190n293 We present a kinematic study of the nuclear stellar disk in M31 at infrared wavelengths using high spatial resolution integral field spectroscopy. The spatial resolution achieved, FWHM = 0.″12 (0.45 pc at the distance of M31), has only previously been equaled in spectroscopic studies by space-based long-slit observations. Using adaptive-optics-corrected integral field spectroscopy from the OSIRIS instrument at the W. M. Keck Observatory, we map the line-of-sight kinematics over the entire old stellar eccentric disk orbiting the supermassive black hole (SMBH) at a distance of r < 4 pc. The peak velocity dispersion is 381 ± 55 km s−1, offset by 0.″13 ± 0.″03 from the SMBH, consistent with previous high-resolution long-slit observations. There is a lack of near-infrared (NIR) emission at the position of the SMBH and young nuclear cluster, suggesting a spatial separation between the young and old stellar populations within the nucleus. We compare the observed kinematics with dynamical... https://escholarship.org/uc/item/2190n293 Thu, 8 Oct 2020 00:00:00 +0000 Lockhart, KE Lu, JR https://orcid.org/0000-0001-9611-0009 Peiris, HV Rich, RM Bouchez, A Ghez, AM https://escholarship.org/uc/item/10c1j6j2 OSIRIS is a near-infrared (1.0–2.4 μm) integral field spectrograph operating behind the adaptive optics system at Keck Observatory and one of the first lenslet-based integral field spectrographs. Since its commissioning in 2005, it has been a productive instrument, producing nearly half the laser guide star adaptive optics papers on Keck. The complexity of its raw data format necessitated a custom data reduction pipeline (DRP) delivered with the instrument in order to iteratively assign flux in overlapping spectra to the proper spatial and spectral locations in a data cube. Other than bug fixes and updates required for hardware upgrades, the bulk of the DRP has not been updated since initial instrument commissioning. We report on the first major comprehensive characterization of the DRP using on-sky and calibration data. We also detail improvements to the DRP, including characterization of the flux assignment algorithm, exploration of spatial rippling in the reduced data cubes,... https://escholarship.org/uc/item/10c1j6j2 Thu, 8 Oct 2020 00:00:00 +0000 Lockhart, Kelly E Do, Tuan https://orcid.org/0000-0001-9554-6062 Larkin, James E https://orcid.org/0000-0001-7687-3965 Boehle, Anna Campbell, Randy D Chappell, Samantha Chu, Devin Ciurlo, Anna https://orcid.org/0000-0001-5800-3093 Cosens, Maren Fitzgerald, Michael P https://orcid.org/0000-0002-0176-8973 Ghez, Andrea Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Lyke, Jim E Mieda, Etsuko Rudy, Alexander R Vayner, Andrey Walth, Gregory Wright, Shelley A https://escholarship.org/uc/item/0ng4n7xk The Quintuplet star cluster is one of only three known young (<10 Myr) massive (M > 104 M⊙) clusters within ∼100 pc of the Galactic center (GC). In order to explore star cluster formation and evolution in this extreme environment, we analyze the Quintuplet’s dynamical structure. Using the HST WFC3-IR instrument, we take astrometric and photometric observations of the Quintuplet covering a 120″ × 120″ field of view, which is 19 times larger than those of previous proper-motion studies of the Quintuplet. We generate a catalog of the Quintuplet region with multiband, near-infrared photometry, proper motions, and cluster membership probabilities for 10,543 stars. We present the radial density profile of 715 candidate Quintuplet cluster members with M ≳ 4.7 M⊙ out to 3.2 pc from the cluster center. A 3σ lower limit of 3 pc is placed on the tidal radius, indicating the lack of a tidal truncation within this radius range. Only weak evidence for mass segregation is found, in contrast... https://escholarship.org/uc/item/0ng4n7xk Thu, 8 Oct 2020 00:00:00 +0000 Rui, Nicholas Z Hosek, Matthew W https://orcid.org/0000-0003-2874-1196 Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Clarkson, William I Anderson, Jay Morris, Mark R https://orcid.org/0000-0002-6753-2066 Ghez, Andrea M https://escholarship.org/uc/item/0gr2k6gw We summarize work on the central parsec of the Galactic center based on imaging and spectroscopic observations at the Keck and Gemini telescopes. These observations include stellar positions in two dimension and the velocity in three dimensions. Spectroscopic observations also enables measurements of the physical properties of individual stars, such as the spectral type and in some cases the effective temperature, metallicity, and surface gravity. These observations show a complex stellar population with a young (4-6 Myr) compact star cluster in the central 0.5 pc embedded in in an older and much more massive nuclear star cluster. Surprisingly, the old late-type giants do not show a cusp profile as long been expected from theoretical work. The majority of the stars have higher than solar metallicity, with only about 6% of the stars having [M/Fe] < -0.5, which is consistent with an origin from the MW disk. https://escholarship.org/uc/item/0gr2k6gw Thu, 8 Oct 2020 00:00:00 +0000 Do, Tuan https://orcid.org/0000-0001-9554-6062 Ghez, Andrea Morris, Mark https://orcid.org/0000-0002-6753-2066 Lu, Jessica https://orcid.org/0000-0001-9611-0009 Chappell, Samantha Feldmeier-Krause, Anja Kerzendorf, Wolfgang Martinez, Gregory David Murray, Norm Winsor, Nathan https://escholarship.org/uc/item/99m3564d A precise extinction law is a critical input when interpreting observations of highly reddened sources such as young star clusters and the Galactic Center (GC). We use Hubble Space Telescope observations of a region of moderate extinction and a region of high extinction to measure the optical and near-infrared extinction law (0.8–2.2 μm). The moderate-extinction region is the young massive cluster Westerlund 1 (Wd1; AKs ∼ 0.6 mag), where 453 proper-motion selected main-sequence stars are used to measure the shape of the extinction law. To quantify the shape, we define the parameter , which behaves similarly to a color-excess ratio, but is continuous as a function of wavelength. The high-extinction region is the GC (AKs ∼ 2.5 mag), where 819 red clump stars are used to determine the normalization of the law. The best-fit extinction law is able to reproduce the Wd1 main-sequence colors, which previous laws misestimate by 10%–30%. The law is inconsistent with a single power law,... https://escholarship.org/uc/item/99m3564d Tue, 25 Sep 2018 00:00:00 +0000 Hosek, Matthew W https://orcid.org/0000-0003-2874-1196 Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Anderson, Jay Do, Tuan https://orcid.org/0000-0001-9554-6062 Schlafly, Edward F https://orcid.org/0000-0002-3569-7421 Ghez, Andrea M Clarkson, William I Morris, Mark R https://orcid.org/0000-0002-6753-2066 Albers, Saundra M https://escholarship.org/uc/item/1ss262s5 The late-type stellar population in the Galactic Center was first predicted to reside in a dynamically relaxed cusp (power law slope ranging from 3/2 to 7/4). However, other works - which rely on models to correct for projection effects - have suggested a flat distribution instead. The need for this correction is due to the lack of information regarding the line-of-sight distances. With a two decade long baseline in astrometric measurements, we are now able to measure significant projected radial accelerations, six of which are newly reported here, which directly constrain line-of-sight distances. Here we present a statistical approach to take advantage of this information and more accurately constrain the shape of the radial density profile of the late-type stellar population in the Galactic Center. https://escholarship.org/uc/item/1ss262s5 Tue, 19 Dec 2017 00:00:00 +0000 Chappell, SN Ghez, AM Do, T https://orcid.org/0000-0001-9554-6062 Martinez, GD Yelda, S Sitarski, BN Lu, JR https://orcid.org/0000-0001-9611-0009 Morris, MR https://orcid.org/0000-0002-6753-2066 https://escholarship.org/uc/item/179199wq We present constraints on the variability and binarity of young stars in the central 10 arcseconds (∼ 0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment's photometric uncertainties, at least 36% of our sample's known early-type stars are variable. We identified eclipsing binary systems by searching for periodic variability. In our sample of spectroscopically confirmed and likely early-type stars, we detected the two previously discovered GC eclipsing binary systems. We derived the likely binary fraction of main sequence, early-type stars at the GC via Monte Carlo simulations of eclipsing binary systems, and find that it is at least 32% with 90% confidence. https://escholarship.org/uc/item/179199wq Tue, 19 Dec 2017 00:00:00 +0000 Gautam, Abhimat K Do, Tuan https://orcid.org/0000-0001-9554-6062 Ghez, Andrea M Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Morris, Mark R https://orcid.org/0000-0002-6753-2066 Sakai, Shoko Witzel, Gunther Sitarski, Breann N Chappell, Samantha https://escholarship.org/uc/item/074831s3 Motion of short-period stars orbiting the supermassive black hole in our Galactic Center has been monitored for more than 20 years. These observations are currently offering a new way to test the gravitational theory in an unexplored regime: in a strong gravitational field, around a supermassive black hole. In this proceeding, we present three results: (i) a constraint on a hypothetical fifth force obtained by using 19 years of observations of the two best measured short-period stars S0-2 and S0-38; (ii) an upper limit on the secular advance of the argument of the periastron for the star S0-2; (iii) a sensitivity analysis showing that the relativistic redshift of S0-2 will be measured after its closest approach to the black hole in 2018. https://escholarship.org/uc/item/074831s3 Tue, 19 Dec 2017 00:00:00 +0000 Hees, A Ghez, AM Do, T Lu, JR https://orcid.org/0000-0001-9611-0009 Morris, MR https://orcid.org/0000-0002-6753-2066 Becklin, EE Witzel, G Boehle, A Chappell, S Chen, Z Chu, D Ciurlo, A https://orcid.org/0000-0001-5800-3093 Dehghanfar, A Gallego-Cano, E Gautam, A Jia, S Kosmo, K Martinez, GD Matthews, K Naoz, S Sakai, S Schödel, R https://escholarship.org/uc/item/9479s1h8 We present new adaptive optics (AO) imaging and spectroscopic measurements of Galactic center source G1 from W. M. Keck Observatory. Our goal is to understand its nature and relationship to G2, which is the first example of a spatially resolved object interacting with a supermassive black hole (SMBH). Both objects have been monitored with AO for the past decade (2003-2014) and are comparatively close to the black hole (a min ∼ 200-300 au) on very eccentric orbits (e G1 ∼ 0.99; e G2 ∼ 0.96). While G2 has been tracked before and during periapsis passage (T 0 ∼ 2014.2), G1 has been followed since soon after emerging from periapsis (T 0 ∼ 2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1's orbital trajectory appears to be in the same plane as that of G2 but with a significantly different argument of periapsis (Δω = 21 ± 4°). This suggests that G1 is an independent object and not part... https://escholarship.org/uc/item/9479s1h8 Tue, 1 Aug 2017 00:00:00 +0000 Witzel, G Sitarski, BN Ghez, AM Morris, MR https://orcid.org/0000-0002-6753-2066 Hees, A Do, T Lu, JR https://orcid.org/0000-0001-9611-0009 Naoz, S Boehle, A Martinez, G Chappell, S Schödel, R Meyer, L Yelda, S Becklin, EE Matthews, K https://escholarship.org/uc/item/6qj3s8tq We give an update of the observations and analysis of G2 - the gaseous red emission-line object that is on a very eccentric orbit around the Galaxy's central black hole and predicted to come within 2400 RS in early 2014. During 2013, the laser guide star adaptive optics systems on the W. M. Keck I and II telescopes were used to obtain three epochs of spectroscopy and imaging at the highest spatial resolution currently possible in the near-IR. The updated orbital solution derived from radial velocities in addition to Br-γ line astrometry is consistent with our earlier estimates. Strikingly, even ~ 6 months before pericenter passage there is no perceptible deviation from a Keplerian orbit. We furthermore show that a proposed "tail" of G2 is likely not associated with it but is rather an independent gas structure. We also show that G2 does not seem to be unique, since several red emission-line objects can be found in the central arcsecond. Taken together, it seems more likely that... https://escholarship.org/uc/item/6qj3s8tq Tue, 1 Aug 2017 00:00:00 +0000 Meyer, L Ghez, AM Witzel, G Do, T https://orcid.org/0000-0001-9554-6062 Phifer, K Sitarski, BN Morris, MR https://orcid.org/0000-0002-6753-2066 Boehle, A Yelda, S Lu, JR https://orcid.org/0000-0001-9611-0009 Becklin, E https://escholarship.org/uc/item/4b98m1n3 We demonstrate that short-period stars orbiting around the supermassive black hole in our Galactic center can successfully be used to probe the gravitational theory in a strong regime. We use 19 years of observations of the two best measured short-period stars orbiting our Galactic center to constrain a hypothetical fifth force that arises in various scenarios motivated by the development of a unification theory or in some models of dark matter and dark energy. No deviation from general relativity is reported and the fifth force strength is restricted to an upper 95% confidence limit of |α|<0.016 at a length scale of λ=150 astronomical units. We also derive a 95% confidence upper limit on a linear drift of the argument of periastron of the short-period star S0-2 of |ω[over ˙]_{S0-2}|<1.6×10^{-3}  rad/yr, which can be used to constrain various gravitational and astrophysical theories. This analysis provides the first fully self-consistent test of the gravitational theory... https://escholarship.org/uc/item/4b98m1n3 Tue, 1 Aug 2017 00:00:00 +0000 Hees, A Do, T https://orcid.org/0000-0001-9554-6062 Ghez, AM Martinez, GD Naoz, S Becklin, EE Boehle, A Chappell, S Chu, D Dehghanfar, A Kosmo, K Lu, JR https://orcid.org/0000-0001-9611-0009 Matthews, K Morris, MR https://orcid.org/0000-0002-6753-2066 Sakai, S Schödel, R Witzel, G https://escholarship.org/uc/item/7zn7567c We present new kinematic measurements and modeling of a sample of 116 young stars in the central parsec of the Galaxy in order to investigate the properties of the young stellar disk. The measurements were derived from a combination of speckle and laser guide star adaptive optics imaging and integral field spectroscopy from the Keck telescopes. Compared to earlier disk studies, the most important kinematic measurement improvement is in the precision of the accelerations in the plane of the sky, which have a factor of six smaller uncertainties (σ10 μas yr-2). We have also added the first radial velocity measurements for eight young stars, increasing the sample at the largest radii (6″-12″) by 25%. We derive the ensemble properties of the observed stars using Monte Carlo simulations of mock data. There is one highly significant kinematic feature (20σ), corresponding to the well-known clockwise disk, and no significant feature is detected at the location of the previously claimed... https://escholarship.org/uc/item/7zn7567c Wed, 12 Jul 2017 00:00:00 +0000 Yelda, S Ghez, AM Lu, JR https://orcid.org/0000-0001-9611-0009 Do, T https://orcid.org/0000-0001-9554-6062 Meyer, L Morris, MR https://orcid.org/0000-0002-6753-2066 Matthews, K https://escholarship.org/uc/item/7b04p0qf We report the detection of the two-dimensional structure of the radio source associated with the Galactic Center black hole, Sagittarius A*, obtained from Very Long Baseline Array observations at a wavelength of 7 mm. The intrinsic source is modeled as an elliptical Gaussian with major-axis size 35.4 × 12.6 RS in position angle 95° east of north. This morphology can be interpreted in the context of both jet and accretion disk models for the radio emission. There is supporting evidence in large angular-scale multi-wavelength observations for both source models for a preferred axis near 95°. We also place a maximum peak-to-peak change of 15% in the intrinsic major-axis size over five different epochs. Three observations were triggered by detection of near infrared (NIR) flares and one was simultaneous with a large X-ray flare detected by NuSTAR. The absence of simultaneous and quasi-simultaneous flares indicates that not all high energy events produce variability at radio wavelengths.... https://escholarship.org/uc/item/7b04p0qf Wed, 12 Jul 2017 00:00:00 +0000 Bower, Geoffrey C Markoff, Sera Brunthaler, Andreas Law, Casey Falcke, Heino Maitra, Dipankar Clavel, M Goldwurm, A Morris, MR https://orcid.org/0000-0002-6753-2066 Witzel, Gunther Meyer, Leo Ghez, AM https://escholarship.org/uc/item/6gb1p4h0 We investigate the orbital motion of the Quintuplet cluster near the Galactic center with the aim of constraining formation scenarios of young, massive star clusters in nuclear environments. Three epochs of adaptive optics high-angular resolution imaging with the Keck/NIRC2 and Very Large Telescope/NAOS-CONICA systems were obtained over a time baseline of 5.8 yr, delivering an astrometric accuracy of 0.5-1 mas yr-1. Proper motions were derived in the cluster reference frame and were used to distinguish cluster members from the majority of the dense field star population toward the inner bulge. Fitting the cluster and field proper motion distributions with two-dimensional (2D) Gaussian models, we derive the orbital motion of the cluster for the first time. The Quintuplet is moving with a 2D velocity of 132 ± 15 km s-1 with respect to the field along the Galactic plane, which yields a three-dimensional orbital velocity of 167 ± 15 km s-1 when combined with the previously known radial... https://escholarship.org/uc/item/6gb1p4h0 Wed, 12 Jul 2017 00:00:00 +0000 Stolte, A Hußmann, B Morris, MR https://orcid.org/0000-0002-6753-2066 Ghez, AM Brandner, W Lu, JR https://orcid.org/0000-0001-9611-0009 Clarkson, WI Habibi, M Matthews, K https://escholarship.org/uc/item/44x17269 We investigate the circumstellar disc fraction as determined from L-band excess observations of the young, massive Arches and Quintuplet clusters residing in the central molecular zone of the Milky Way. The Quintuplet cluster was searched for L-band excess sources for the first time. We find a total of 26 excess sources in the Quintuplet cluster, and 21 sources with L-band excesses in the Arches cluster, of which 13 are new detections. With the aid of proper motion membership samples, the disc fraction of the Quintuplet cluster could be derived for the first time to be 4.0 ± 0.7%. There is no evidence for a radially varying disc fraction in this cluster. In the case of the Arches cluster, a disc fraction of 9.2 ± 1.2% approximately out to the cluster's predicted tidal radius, r< 1.5 pc, is observed. This excess fraction is consistent with our previously found disc fraction in the cluster in the radial range 0.3 ⊙, as derived from J-band photospheric magnitudes. We discuss the... https://escholarship.org/uc/item/44x17269 Wed, 12 Jul 2017 00:00:00 +0000 Stolte, A Hußmann, B Olczak, C Brandner, W Habibi, M Ghez, AM Morris, MR https://orcid.org/0000-0002-6753-2066 Lu, JR https://orcid.org/0000-0001-9611-0009 Clarkson, WI Anderson, J https://escholarship.org/uc/item/9fg6382p After recent sensitivity upgrades at the Keck Interferometer (KI), systematic interferometric 2 μm studies of the innermost dust in nearby Seyfert nuclei are within observational reach. Here, we present the analysis of new interferometric data of NGC4151, discussed in context of the results from recent dust reverberation, spectro-photometric, and interferometric campaigns. The complete data set gives a complex picture, in particular the measured visibilities from now three different nights appear to be rather insensitive to the variation of the nuclear luminosity. KI data alone indicate two scenarios: the K-band emission is either dominated to ∼ 90% by size scales smaller than 30 mpc, which falls short of any dust reverberation measurement in NGC4151 and of theoretical models of circum-nuclear dust distributions. Or contrary, and more likely, the K-band continuum emission is dominated by hot dust (≳1300 K) at linear scales of about 50 mpc. The linear size estimate varies by a... https://escholarship.org/uc/item/9fg6382p Tue, 20 Jun 2017 00:00:00 +0000 Pott, Jorg-Uwe Malkan, Matt A https://orcid.org/0000-0001-6919-1237 Elitzur, Moshe Ghez, Andrea M Herbst, Tom M Schödel, Rainer Woillez, Julien https://escholarship.org/uc/item/01t2t06s Owing to its extremely high luminosity and long duration, supernova (SN) 2006gy radiated more energy in visual light than any other known SN. Two hypotheses to explain its high luminosity at early times - that it was powered by shock interaction with circumstellar material (CSM) as implied by its Type IIn spectrum, or that it was fueled by radioactive decay from a large mass of 56Ni synthesized in a pair-instability SN-predicted different late-time properties. Here we present observations of SN 2006gy obtained more than a year after discovery. We were unable to detect it at visual wavelengths, but clear near-infrared (IR) K′ and H-band detections show that it is still at least as luminous as the peak of a normal Type II SN. We also present spectra giving an upper limit to the late-time Ha luminosity of ≲S10 39 erg s-1. Based on the weak late-time Ha, X-ray, and radio emission, combined with the difficulty of explaining the shift to IR wavelengths, we can rule out ongoing CSM interaction... https://escholarship.org/uc/item/01t2t06s Tue, 20 Jun 2017 00:00:00 +0000 Smith, Nathan Foley, Ryan J https://orcid.org/0000-0002-2445-5275 Bloom, Joshua S Li, Weidong Filippenko, Alexei V https://orcid.org/0000-0003-3460-0103 Gavazzi, Raphaël Ghez, Andrea Konopacky, Quinn Malkan, Matthew A https://orcid.org/0000-0001-6919-1237 Marshall, Philip J Pooley, David Treu, Tommaso https://orcid.org/0000-0002-8460-0390 Woo, Jong-Hak https://escholarship.org/uc/item/6842h9bf We present 3D kinematic observations of stars within the central 0.5 pc of the Milky Way nuclear star cluster using adaptive optics imaging and spectroscopy from the Keck telescopes. Recent observations have shown that the cluster has a shallower surface density profile than expected for a dynamically relaxed cusp, leading to important implications for its formation and evolution. However, the true three dimensional profile of the cluster is unknown due to the difficulty in de-projecting the stellar number counts. Here, we use spherical Jeans modeling of individual proper motions and radial velocities to constrain for the first time, the de-projected spatial density profile, cluster velocity anisotropy, black hole mass ($M_\mathrm{BH}$), and distance to the Galactic center ($R_0$) simultaneously. We find that the inner stellar density profile of the late-type stars, $\rho(r)\propto r^{-\gamma}$ to have a power law slope $\gamma=0.05_{-0.60}^{+0.29}$, much more shallow than the... https://escholarship.org/uc/item/6842h9bf Wed, 1 Mar 2017 00:00:00 +0000 Do, T https://orcid.org/0000-0001-9554-6062 Martinez, GD Yelda, S Ghez, A Bullock, J Kaplinghat, M https://orcid.org/0000-0001-8555-0164 Lu, JR https://orcid.org/0000-0001-9611-0009 Peter, AHG Phifer, K https://escholarship.org/uc/item/1nr6b6b7 At a projected distance of ∼26 pc from Sgr A∗, the Arches cluster provides insight into star formation in the extreme Galactic center (GC) environment. Despite its importance, many key properties, such as the cluster's internal structure and orbital history, are not well known. We present an astrometric and photometric study of the outer region of the Arches cluster (R > 6.″25) using Hubble Space Telescope WFC3IR. Using proper motions, we calculate membership probabilities for stars down to F153M = 20 mag (∼2.5 Mo) over a 120″ × 120″ field of view, an area 144 times larger than previous astrometric studies of the cluster. We construct the radial profile of the Arches to a radius of 75″ (∼3 pc at 8 kpc), which can be well described by a single power law. From this profile we place a 3σ lower limit of 2.8 pc on the observed tidal radius, which is larger than the predicted tidal radius (1-2.5 pc). Evidence of mass segregation is observed throughout the cluster, and no tidal tail... https://escholarship.org/uc/item/1nr6b6b7 Tue, 25 Oct 2016 00:00:00 +0000 Hosek, Matthew W https://orcid.org/0000-0003-2874-1196 Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Anderson, Jay Ghez, Andrea M Morris, Mark R https://orcid.org/0000-0002-6753-2066 Clarkson, William I https://escholarship.org/uc/item/8sq9c4jq We present new near-infrared spectroscopic observations of the outer edges of the young stellar cluster around the supermassive black hole at the Galactic center. The observations show a break in the surface density profile of young stars at ∼13″ (0.52 pc). These observations spectroscopically confirm previous suggestions of a break based on photometry. Using Gemini Norths Near-Infrared Integral Field Spectrometer, we are able to detect and separate early- and late-type stars with a 75% completeness at Ks = 15.5.We sample a region with radii between 7″ and 23″ (0.28-0.92 pc) from Sgr A∗-and present new spectral classifications of 144 stars brighter than Ks = 15.5, where 140 stars are late-type (>1Gyr) and only four stars are early-type (young, 4-6Myr). A broken power-law fit of the early-type surface-density matches well with our data and previously published values. The projected surface-density of late-type stars is also measured and found to be consistent with previous results.... https://escholarship.org/uc/item/8sq9c4jq Tue, 27 Sep 2016 00:00:00 +0000 Støstad, M Do, T Murray, N Lu, JR https://orcid.org/0000-0001-9611-0009 Yelda, S Ghez, A https://escholarship.org/uc/item/7kc2v20t We report new observations of the Galactic Center source G2 from the W. M. Keck Observatory. G2 is a dusty red object associated with gas that shows tidal interactions as it nears its closest approach with the Galaxy's central black hole. Our observations, conducted as G2 passed through periapse, were designed to test the proposal that G2 is a 3 Earth mass gas cloud. Such a cloud should be tidally disrupted during periapse passage. The data were obtained using the Keck II laser guide star adaptive optics system (LGSAO) and the facility near-infrared camera (NIRC2) through the K′ [2.1 μm] and L′ [3.8 μm] broadband filters. Several results emerge from these observations: (1) G2 has survived its closest approach to the black hole as a compact, unresolved source at L′, (2) G2's L′ brightness measurements are consistent with those over the last decade, (3) G2's motion continues to be consistent with a Keplerian model. These results rule out G2 as a pure gas cloud and imply that G2... https://escholarship.org/uc/item/7kc2v20t Tue, 21 Jul 2015 00:00:00 +0000 Witzel, G Ghez, AM Morris, MR https://orcid.org/0000-0002-6753-2066 Sitarski, BN Boehle, A Naoz, S Campbell, R Becklin, EE Canalizo, G Chappell, S Do, T https://orcid.org/0000-0001-9554-6062 Lu, JR https://orcid.org/0000-0001-9611-0009 Matthews, K Meyer, L Stockton, A Wizinowich, P Yelda, S https://escholarship.org/uc/item/0n5609vt We present a metallicity analysis of 83 late-type giants within the central 1 pc of the Milky Way. K-band spectroscopy of these stars was obtained with the medium spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guided star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is a large variation in the metallicity, with stars ranging from [M/H] < -1.0 to above solar metallicity. About 6% of the stars have [M/H] < -0.5. This result is in contrast to previous observations with smaller samples that show stars at the Galactic center having approximately solar metallicity with only small variations. Our current measurement uncertainties are dominated by systematics in the model, especially at [M/H] > 0, where there are stellar lines not represented in the model. However, the conclusion that there are low-metallicity stars, as well as large variations in metallicity, is robust. The metallicity... https://escholarship.org/uc/item/0n5609vt Thu, 9 Jul 2015 00:00:00 +0000 Do, Tuan https://orcid.org/0000-0001-9554-6062 Kerzendorf, Wolfgang Winsor, Nathan Støstad, Morten Morris, Mark R https://orcid.org/0000-0002-6753-2066 Lu, Jessica R https://orcid.org/0000-0001-9611-0009 Ghez, Andrea M