IRS 16SW - A New Comoving Group of Young Stars in the Central Parsec of the Milky Way

One of the most perplexing problems associated with the supermassive black hole at the center of our Galaxy is the origin of the young stars in its close vicinity. Using proper motion measurements and stellar number density counts based on 9 years of diffraction-limited K(2.2 micron)-band speckle imaging at the W. M. Keck 10-meter telescopes, we have identified a new comoving group of stars, which we call the IRS 16SW comoving group, located 1.9" (0.08 pc, in projection) from the central black hole. Four of the five members of this comoving group have been spectroscopically identified as massive young stars, specifically He I emission-line stars and OBN stars. This is the second young comoving group within the central parsec of the Milky Way to be recognized and is the closest, by a factor of 2, in projection to the central black hole. These comoving groups may be the surviving cores of massive infalling star clusters that are undergoing disruption in the strong tidal field of the central supermassive black hole.Comment: 10 pages, 1 figure, accepted for ApJL, uses emulateap

Galactic Center Youth: Orbits and Origins of the Young Stars in the Central Parsec

We present new proper motions for the massive, young stars at the Galactic Center, based on 10 years of diffraction limited data from the Keck telescopes. Our proper motion measurements now have uncertainties of only 1-2 km/s and allow us to explore the origin of the young stars that reside within the sphere of inflience of the supermassive black hole whose strong tidal forces make this region inhospitable for star formation. Their presence, however, may be explained either by in situ star formation in an accretion disk or as the remnants of a massive stellar cluster which spiraled in via dynamical friction. Earlier stellar velocity vectors were used to postulate that all the young stars resided in two counter-rotating stellar disks, which is consistent with both of the above formation scenarios. Our precise proper motions allow us, for the frst time, to determine the orbital parameters of each individual star and thereby to test the hypothesis that the massive stars reside in two stellar disks. Of the 26 young stars in this study that were previously proposed to lie on the inner, clockwise disk, we find that nearly all exhibit orbital constraints consistent with such a disk. On the other hand, of the 7 stars in this study previously proposed to lie in the outer, less well-defhed counter-clockwise disk, 6 exhibit inclinations that are inconsistent with such a disk, bringing into question the existence of the outer disk. Furthermore, for stars in the inner disk that have eccentricity constraints, we find several that have lower limits to the eccentricity of more than 0.4, implying highly eccentric orbits. This stands in contrast to simple accretion disk formation scenarios which typically predict predominantly circular orbits

Spectral synthesis of circumstellar disks - application to white dwarf debris disks

Gas and dust disks are common objects in the universe and can be found around various objects, e.g. young stars, cataclysmic variables, active galactic nuclei, or white dwarfs. The light that we receive from disks provides us with clues about their composition, temperature, and density. In order to better understand the physical and chemical dynamics of these disks, self-consistent radiative transfer simulations are inevitable. Therefore, we have developed a 1+1D radiative transfer code as an extension to the well-established model atmosphere code \verb!PHOENIX!. We will show the potential of the application of our code to model the spectra of white dwarf debris disks.Comment: 4 pages, 4 figures, to appear in: Proceedings of the 16th European Workshop on White Dwarf

Infrared and radio observations of W51: Another Orion-KL at a distance of 7kpc

The bright infrared sources W51-IRS2 has at least three components with different physical and evolutionary properties. The spatial distribution and the near infrared spectra of the components in IRS2 are remarkably similar to, but more luminous than those found in Orion, where an H2 region of comparable linear size is also located close to a cluster of compact infrared sources. The characteristics of the nearby W51-NORTH H2O maser source, and the detection of 2 micro m H2 quadrupole emission in IRS2 indicate that the mass loss phenomena found in Orion-KL also exist in W51

High Proper Motion Stars in the Vicinity of Sgr A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy

Over a two year period (1995-1997), we have conducted a diffraction-limited imaging study at 2.2 microns of the inner 6"x6" of the Galaxy's central stellar cluster using the Keck 10-m telescope. The K band images obtained reveal a large population of faint stars. We use an unbiased approach for identifying and selecting stars to be included in this proper motion study, which results in a sample of 90 stars with brightness ranging from K=9-17 and velocities as large as 1,400+-100 km/sec. Compared to earlier work (Eckart et al. 1997; Genzel et al. 1997), the source confusion is reduced by a factor of 9, the number of stars with proper motion measurement in the central 25 arcsec^2 of our galaxy is doubled, and the accuracy of the velocity measurements in the central 1 arcsec^2 is improved by a factor of 4. The peaks of both the stellar surface density and the velocity dispersion are consistent with the position of the unusual radio source and blackhole candidate, Sgr A*, suggesting that Sgr A* is coincident (+-0."1) with the dynamical center of the Galaxy. As a function of distance from Sgr A*, the velocity dispersion displays a falloff well fit by Keplerian motion about a central dark mass of 2.6(+-0.2)x10^6 Mo confined to a volume of at most 10^-6 pc^3, consistent with earlier results. Although uncertainties in the measurements mathematically allow for the matter to be distributed over this volume as a cluster, no realistic cluster is physically tenable. Thus, independent of the presence of Sgr A*, the large inferred central density of at least 10^12 Mo/pc^3, which exceeds the volume-averaged mass densities found at the center of any other galaxy, leads us to the conclusion that our Galaxy harbors a massive central black hole.Comment: 19 pages, 8 figures, accepted for publications in the Astrophysical Journa

APM 08279+5255: Keck Near- and Mid-IR High-Resolution Imaging

We present Keck high-resolution near-IR (2.2 microns; FWHM~0.15") and mid-IR (12.5 microns; FWHM~0.4") images of APM08279+5255, a z=3.91 IR-luminous BALQSO with a prodigious apparent bolometric luminosity of 5x10^{15} Lsun, the largest known in the universe. The K-band image shows that this system consists of three components, all of which are likely to be the gravitationally lensed images of the same background object, and the 12.5 micron image shows a morphology consistent with such an image configuration. Our lens model suggests that the magnification factor is ~100 from the restframe UV to mid-IR, where most of the luminosity is released. The intrinsic bolometric luminosity and IR luminosity of APM08279+5255 are estimated to be 5x10^{13} Lsun and 1x10^{13} Lsun, respectively. This indicates that APM 08279+5255 is intriniscally luminous, but it is not the most luminous object known. As for its dust contents, little can be determined with the currently available data due to the uncertainties associated with the dust emissivity and the possible effects of differential magnification. We also suggest that the lensing galaxy is likely to be a massive galaxy at z~3.Comment: 32 pages, 4 tables, 11 figures; Accepted for publication in Ap

First Science Results From SOFIA/FORCAST: Super-Resolution Imaging of the S140 Cluster at 37\micron

We present 37\micron\ imaging of the S140 complex of infrared sources centered on IRS1 made with the FORCAST camera on SOFIA. These observations are the longest wavelength imaging to resolve clearly the three main sources seen at shorter wavelengths, IRS 1, 2 and 3, and are nearly at the diffraction limit of the 2.5-m telescope. We also obtained a small number of images at 11 and 31\micron\ that are useful for flux measurement. Our images cover the area of several strong sub-mm sources seen in the area -- SMM 1, 2, and 3 -- that are not coincident with any mid-infrared sources and are not visible in our longer wavelength imaging either. Our new observations confirm previous estimates of the relative dust optical depth and source luminosity for the components in this likely cluster of early B stars. We also investigate the use of super-resolution to go beyond the basic diffraction limit in imaging on SOFIA and find that the van Cittert algorithm, together with the "multi-resolution" technique, provides excellent results