The S-star cluster at the center of the Milky Way

Sabha, Nesrin; Eckart, A.; Merritt, David; Zamaninasab, M.; Witzel, G.; García-Marín, M.; Jalali, B.; Valencia-S., M.; Yazici, S.; Shahzamanian, B.; Straubmeier, C.

doi:10.1051/0004-6361/201219203

Cited by 49 publications

(68 citation statements)

References 61 publications

(98 reference statements)

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“…As explained in Sabha et al (2012), the live time of these blend stars (also indicated through observations) is about 3 years during which they dissolve again into individual objects with flux densities below the confusion limit due to their proper motions. If one aims to explain the 2007−2012 K s -band identifications of the DSO by blend stars, one requires about 2−3 of these transient apparent objects.…”

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 77%

“…We can therefore consider the likelihood of finding faint stars above the confusion limit at the position of the DSO over a time span of several years. From the KLF analysis by Sabha et al (2010Sabha et al ( , 2012 we infer a maximum of about 40 stars fainter than 16 magnitudes (dereddened) within the central 1.3 × 1.3 . This implies 0.2 sources per resolution element and observing epoch.…”

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 94%

“…With two independent methods we determined the central K s -band confusion limit observationally. Sabha et al (2010Sabha et al ( , 2012 employed successive subtraction of stars in the S-star cluster. Witzel et al (2012) used the shape of the SgrA* flare amplitude histogram.…”

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 99%

“…The result of the statistical investigation of the S-star cluster by Sabha et al (2012) is that for a range of observationally supported parameters that describe the structure and luminosity function of the cluster, the authors can give the probability of finding a blend star in a single spatial resolution element above the confusion limit. Here we use a power law index of the projected spatial distribution of α = 0.30 ± 0.05 and a K-band luminosity function exponent of KLF = 0.18 ± 0.07.…”

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 99%

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Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic center

Eckart¹,

Mužić²,

Yazici³

et al. 2013

A&A

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152

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Context. There are a number of faint compact infrared excess sources in the central stellar cluster of the Milky Way. Their nature and origin is unclear. In addition to several isolated objects of this kind there is a small but dense cluster of comoving sources (IRS13N) located ∼3 west of SgrA* just 0.5 north of the bright IRS13E cluster of Wolf-Rayet and O-type stars. Based on the analysis of their color and brightness, there are two main possibilities: (1) they may be dust-embedded stars older than a few Myr; or (2) very young, dusty stars with ages younger than 1 Myr. Aims. We present a first K s -band identification and proper motions of the IRS13N members, the high-velocity dusty S-cluster object (DSO, also referred to as G2), and other infrared excess sources in the central field. Goal is to constrain the nature of these source. Methods. The L -(3.8 μm) K s -(2.2 μm) and H-band (1.65 μm) observations were carried out using the NACO adaptive optics system at the ESO VLT. Proper motions were obtained by linear fitting of the stellar positions extracted by StarFinder as a function of time, weighted by positional uncertainties, and by Gaussian fitting from high-pass filtered and deconvolved images. We also present results of near-infrared (NIR) H-and K s -band ESO-SINFONI integral field spectroscopy of the Galactic center cluster ISR13N. Results. We show that within the uncertainties, the positions and proper motions of the IRS13N sources in K s -and L -band are identical. The HK−sL colors then indicate that the bright L -band IRS13N sources are indeed dust-enshrouded stars rather than core-less dust clouds. The proper motions also show that the IRS13N sources are not strongly gravitationally bound to each other. Combined with their NIR colors, this implies that they have been formed recently. For the DSO we obtain proper motions and a K s -L -color. Conclusions. Most of the compact L -band excess emission sources have a compact H-or K s -band counterpart and therefore are likely stars with dust shells or disks. Our new results and orbital analysis from our previous work favor the hypothesis that the infrared excess IRS13N members and other dusty sources close to SgrA* are young dusty stars and that star formation at the Galactic center (GC) is a continuously ongoing process. For the DSO the color information indicates that it may be a dust cloud or a dust-embedded star.

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Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 77%

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 94%

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 99%

Section: Statistical Robustness Of the Dso Identificationsmentioning

confidence: 99%

See 2 more Smart Citations

Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic center

Eckart¹,

Mužić²,

Yazici³

et al. 2013

A&A

Self Cite

152

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“…Since the eccentricity of S2 is the largest among the three stars, it is currently the star best suited for the determination of the relativistic parameter. This result must be seen in the light of the discussion of the resonant relaxation within the central star cluster close to Sgr A* (Rauch & Tremaine 1996;Alexander 2005;Hopman & Alexander 2006;Merritt et al 2010;Kocsis & Tremaine 2011;Sabha et al 2012). Sabha et al (2012) investigate the effects of the orbital torques on the orbit of S2 due to the resonant relaxation.…”

Section: Resultsmentioning

confidence: 99%

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

Parsa

Eckart

Shahzamanian

et al. 2017

ApJ

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110

120

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The S-star cluster in the Galactic center allows us to study the physics close to a supermassive black hole, including distinctive dynamical tests of general relativity. Our best estimates for the mass of and the distance to Sgr A* using the three stars with the shortest period (S2, S38, and S55/S0-102) and Newtonian models are M BH = (4.15 ± 0.13 ± 0.57) × 10 6 M and R 0 = 8.19 ± 0.11 ± 0.34 kpc. Additionally, we aim at a new and practical method to investigate the relativistic orbits of stars in the gravitational field near Sgr A*. We use a first-order post-Newtonian approximation to calculate the stellar orbits with a broad range of periapse distance r p . We present a method that employs the changes in orbital elements derived from elliptical fits to different sections of the orbit. These changes are correlated with the relativistic parameter defined as Υ ≡ r s /r p (with r s being the Schwarzschild radius) and can be used to derive Υ from observational data. For S2 we find a value of Υ = 0.00088 ± 0.00080, which is consistent, within the uncertainty, with the expected value of Υ = 0.00065 derived from M BH and the orbit of S2. We argue that the derived quantity is unlikely to be dominated by perturbing influences such as noise on the derived stellar positions, field rotation, and drifts in black hole mass.

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A stellar fly‐by close to the Galactic center: Can we detect stars on highly relativistic orbits?

Tursunov

2018

Astron Nachr

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The Galactic center Nuclear Star Cluster is one of the densest stellar clusters in the Galaxy. The stars in its inner portions orbit the supermassive black hole associated with the compact radio source Sgr A* at the orbital speeds of several thousand kilometers per second. The B‐type star S2 is currently the best case to test the general relativity as well as other theories of gravity, based on its stellar orbit. Yet, its orbital period of ∼16 years and the eccentricity of ∼0.88 yields the relativistic pericenter shift of ∼11′, which is observationally still difficult to reliably measure due to possible Newtonian perturbations as well as reference‐frame uncertainties. A naive way to solve this problem is to find stars with smaller pericenter distances, rp ≲ 1529 Schwarzschild radii (120 AU), and thus with more prominent relativistic effects. In this paper, we show that to detect stars on relativistic orbits is progressively less likely, given the volume shrinkage and the expected stellar density distributions. Finally, one arrives at a sparse region where the total number of bright stars is expected to fall below 1. One can, however, still potentially detect stars crossing this region. In this paper, we provide a simple formula for the detection probability of a star crossing a sparse region. We also examine an approximate timescale in which the star reappears in the sparse region, i.e., a “waiting” timescale for observers.

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The S-star cluster at the center of the Milky Way

Cited by 49 publications

References 61 publications

Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic center

Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic center

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

A stellar fly‐by close to the Galactic center: Can we detect stars on highly relativistic orbits?

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