S. Drapatz

The Nuclear Cluster of the Milky Way: Star Formation and Velocity Dispersion in the Central 0.5 Parsec

We report the first results of an extensive new study of the Galactic center stellar cluster. The central parsec is powered by a cluster of about two dozen luminous and helium-rich blue supergiants/Wolf-Rayet stars (Teff ~ 20,000-30,000 K) with ZAMS masses up to ~100 M☉. The most likely scenario for the formation of the massive stars is a small star formation burst between 3 × 106 and 7 × 106 years ago. In this scenario the Galactic center is presently in a short-lived, post-main-sequence wind phase. In addition, there is evidence for another star formation event about 108 years ago, as well as for recently formed massive stars that may have been transported into the central core along with orbiting gas streamers. The radial velocity dispersion of 35 early- and late-type stars with distances of 1-12 from Sgr A* is 154 ± 19 km s-1. Our new results strongly favor the existence of a central dark mass of ~3 × 106 M☉ (density ≥ 108.5 M☉ pc-3, M/L ≥ 10 M☉/L☉) within 0.14 pc of the dynamic center.

A cluster of He I emission-line stars in the Galactic center

We report 1″.9/300 km s −1 resolution imaging spectroscopy of He I n=2 1 P→n=2 1 S 2.06 μm line emission in the Galactic center. There is a group of about a dozen compact, broad-line He I emission-line stars most of which are positionally coincident with compact 2 μm continuum sources. IRS 16 and its broad-line region is probably a central concentration of this 1 pc diameter He I star cluster. The He I stars may be blue supergiants with heavy mass loss. The high He I/H I (Brα, Brγ) ratios suggest an overabundance of helium in their atmospheres indicative of a post-main-sequence phase.

Near-infrared line imaging of NGC 6240 : collision shock and nuclear starburst

Images of the merging luminous IR galaxy NGC 6240 in the H 2 v=1→0 S(1) 2.12 μm line and the [Fe II] 1.64 μm line are presented, together with velocity-resolved slit spectra of these lines. The images have an angular resolution of ≤1″, and for the H 2 line, images in three adjacent 320 km s −1 wide velocity intervals are presented. The H 2 emission does not follow the stellar light and shows no trace of the two nuclei of the galaxy. Instead, it peaks between these nuclei. The H 2 emission extends over ∼5 kpc and shows a complex morphology and velocity structure in its outer parts

Subarcsecond mid-infrared imaging of warm dust in the narrow-line region of NGC 1068

Subarcsecond 8 and 10 μm and diffraction-limited 19 μm imaging of the inner few hundred parsecs of the Seyfert nucleus in NGC 1068 shows the emission to be extended over a region of ∼70×140 pc. In particular, 10.3 μm images with spatial resolutions of 0″.5 or better reveal that the warm dust is associated with the narrow-line clouds and is probably partially mixed with the photoionized gas. Extinction considerations, however, imply that the bulk of the warm dust is located deeper in neighboring molecular clouds, the exposed surfaces of which form the narrow-line clouds

Airborne infrared spectroscopy of Comet Wilson (1986l) and comparisons with Comet Halley

H/sub 2/O and possibly CH/sub 4/ have been detected in near-infrared spectra of Comet Wilson (1986l). The observed number and relative intensities of cometary H/sub 2/O lines in the nu3 band at 2.65 microns were consistent with fluorescent excitation pumped by solar infrared photons. The H/sub 2/O production rate in Comet Wilson was approximately 3 x 10 to the 29th/s at R = 1.2 AU; no pronounced temporal variability was observed. Lines in the nu3 band of CH/sub 4/ at 3.3 microns were possibly detected at the 3 sigma confidence level. The CH/sub 4/ abundance is in the range CH/sub 4//H/sub 2/O = 0.014-0.045; the uncertainty is due primarily to the assumed effective excitation temperature of CH/sub 4/. The CH/sub 4/ abundance in this dynamically new comet is similar to that observed in P/Halley. These values are low for equilibrium compositional models and very high for disequilibrium condensation in the solar nebula. 35 references.

High-resolution imaging of forbidden Fe II 1.64 microns, Brackett-gamma, and H2 1-0 S(1) emission in the starburst galaxy NGC 253

We present 1″ resolution imaging of the nuclear region of the starburst galaxy NGC 253 in the near-infrared lines of [Fe II] 1.64 μm, Brackett-γ, and H 2 1-0 S(1), together with the adjacent continuum. The data reveal an emission region extended some 10″ northeast of the nucleus, with several embedded compact peaks or hot spots. The continuum and the three spectral lines have the same general distribution but differ in detail. The line emission from H 2 and Brγ are closely matched in the circumnuclear region. However, the H 2 emission reveals wispy structures which are more prominent to the northwest of the nucleus

High-resolution imaging of Brackett-gamma and H2 1-0 S(1) emission in the Seyfert galaxy NGC 1068

This paper reports 1-arcsec resolution imaging of 2-micron H I Br-gamma and H2 1-0 S(1) line emission toward the nucleus of the Seyfert 2 galaxy NGC 1068. The data, taken with a new imaging Fabry-Perot, show that the emission in both infrared lines originates from within 2 arcsec (170 pc) of the peak of radio, near-infrared, and visible continuum radiation. The vibrational H2 emission has a double-lobed shape, with a minimum toward the nucleus and two peaks about 1.3 arcsec on either side of the nucleus along position angle 70 deg east of north. In contrast, the Br-gamma emission is peaked on the nucleus, similar to the central radio continuum structure and the narrow-line region (NLR) in the visible. The Br-gamma emission has an about 1 arcsec (FWHM) diameter and is more compact than the distributions of visible NLR tracers. The H2 emission is probably produced in hot gas with mass a few 1000 solar masses. However, the total H2 mass in the circumnuclear region hydrogen may approach 10 to the 8th solar masses. The H2 emission is not produced in a 1-pc size obscuring torus but probably comes from a system of molecular clouds in the vicinity of themorexa0» NLR. The molecular clouds probably contribute significantly to the extinction of the nuclear source. It is proposed that the circumnuclear Br-gamma and H2 emission lines are excited in gas heated by UV or X-ray photons emitted by a central nonstellar source. 35 refs.«xa0less

3D - a new generation imaging spectrometer

3D, the next generation near-IR spectrometer developed at the MPE, offers, in a single integration, the opportunity to image an 8 x 8 field with a pixel scale of 0.5 or 0.3 across the entire K- or H-band simultaneously at a spectral resolution of R equals 1000 or R equals 2000 (K). Combining the advantages of imaging and spectroscopy increases the observing efficiency on small extended objects (e.g., galactic nuclei) by such a large factor over existing grating or Fabry-Perot spectrometers that subarcsecond near-IR spectroscopy on faint Seyferts, starbursts, quasars, or distant galaxies clusters becomes feasible for the first time on 4 m class telescopes. 3D, including a NICMOS III FPA at 25 e-/single read, has been successfully operated at telescopes such as the 4.2 m WHT, 3.5 m Calar Alto, and 2.2 m La Silla. An additional tip-tilt seeing corrector for 3D called ROGUE correcting on up to 18th mag stars at 4 m-class-telescopes was successfully commissioned in the summer of 1994. The optical and electronic design of 3D as well as recent results are presented.

First Results from ISO Spectra of Supernova Remnants Heavily Interacting with the ISM

ISO spectra 1 of the supernova remnant RCW103 are presented. This object is the prototype of a SNR shock heavily interacting with dense ISM (probably a molecular cloud). The spectra are dominated by prominent lines and show very little continuum at < 40 m suggesting that the 12 and 25 m IRAS emission from these types of remnant could be dominated by lines rather than continuum emission from warm dust heated by the shock as generally believed. The ISO data provide for the rst time a simple and reliable estimate of the gas phase abundances of Si and Fe which are found to be close to solar relative to non refractory species such as Ne, S and Ar. This indicates that the shock is very eeective in destroying the ISM dust and may therefore explain the absence of warm dust behind the shock. Like the optical Nickel lines, NiII]6.63 m yields Ni/Fe abundances a factor 10 above solar which we conclude results from a large underestimation of the computed Ni + collision strengths. 1 Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA. 2 E. OLIVA ET AL.

Observing the Galactic Center with the VLTI

Recent observations of the Galactic Center have resulted in the detection of stellar proper motions in the innermost core of the Galaxy. After 4 years of high resolution near-infrared imaging we have determined proper motions for 39 stars between 0.03 and 0.3 pc from the compact radio source SgrA*. Proper motion and radial velocity dispersions are in very good agreement indicating that the stellar velocity field on average is close to isotropic. We have detected significant changes in the structure of the innermost complex of stars in the vicinity of SgrA*, suggesting stellar motions of >10 km/s within Taking radial and proper motion data together we find a 2.45(±0.4)×106 M⊙ central dark mass within < 0.015 pc of SgrA*. The density of this central dark mass therefore is in excess of 1012 M⊙pc-3, implying that the central mass concentration is likely a single massive black hole.