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

Abstract

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.

Clump formation through colliding stellar winds in the Galactic Centre

“…The tidal disruption of this cloud is being monitored by different groups (e.g., Eckart et al 2013;Gillessen et al 2013;Phifer et al 2013) and provides a unique opportunity to test accretion physics, due to both its proximity and the timescale on which it happens. Gillessen et al (2012) estimated the mass of G2 to be ∼ 3 M⊕ from its line emission.…”

Hydrodynamical simulations of a compact source scenario for G2

“…The object has been detected in the L-band with the infrared imager NACO and with the integral field spectrograph SINFONI at the VLT in Brackett-γ, He I and Paschen-α line emission. The detection in these bands has also been confirmed by Eckart et al (2013) and Phifer et al (2013), even if the nature of this object is still controversial. With the help of observations from the last 10 yr, Gillessen et al (2012) and Gillessen et al (2013a,b) derived the dynamical properties of the object, finding that G2 is orbiting around the supermassive black-hole on a very eccentric orbit (e≈ 0.98), with pericenter at 2400 Schwarzschild radii, which G2 is expected to reach in early 2014.…”

Polarization: A Method to Reveal the True Nature of the Dusty S-Cluster Object (DSO/G2)

“…The increase of a Brγ line width also shows that it is a young accreting star surrounded by a dusty envelope [8]. It is an infrared-excess source compared to the main-sequence stars and has a magnitude of 18.5 in K s -band (2.2 µm) continuum [6,9]. Since it is a very faint source in a crowded stellar region, it is not easy to disentangle its emission from the stars around it, therefore one needs to consider all its properties such as spectral properties, orbital dynamics, and polarimetry in order to conclude on its nature.…”

“…The Dusty S-cluster Object (DSO/G2) is a peculiar source in the Galactic centre which orbits on a highly eccentric orbit around Sagittarius A* (Sgr A*) which is associated with a super-massive black hole M BH 4 × 10 6 M [1-4]. It has been described as a core-less dusty gas cloud named as G2 [5] and also as a Dusty S-cluster Object (DSO) with a stellar nature [6]. This source has been of great interest since its periapse distance is only 2000 Schwarzschild radii.…”