arXiv subjects

A. Damineli

Publications and source records attributed to A. Damineli.

43 records · Page 3Linked to original sources

arXiv2002

The Stellar Content of Obscured Galactic Giant H II Regions IV.: NGC3576

We present deep, high angular resolution near-infrared images of the obscured Galactic Giant H II region NGC3576. Our images reach objects to ~3M_sun. We collected high signal-to-noise K-band spectra of eight of the brightest objects, some of which are affected by excess emission and some which follow a normal interstellar reddening law. None of them displayed photospheric features typical of massive OB type stars. This indicates that they are still enshrouded in their natal cocoons. The K-band brightest source (NGC3576 #48) shows CO 2.3 micron bandhead emission, and three others have the same CO feature in absorption. Three sources display spatially unresolved H_2 emission, suggesting dense shocked regions close to the stars. We conclude that the remarkable object NGC3576 #48 is an early-B/late-O star surrounded by a thick circumstellar disk. A number of other relatively bright cluster members also display excess emission in the K-band, indicative of reprocessing disks around massive stars (YSOs). Such emission appears common in other Galactic Giant H II regions we have surveyed. The IMF slope of the cluster, Gamma = -1.51, is consistent with Salpeter's distribution and similar to what has been observed in the Magellanic Cloud clusters and in the periphery of our Galaxy.

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arXiv2002

A Near-Infrared Survey for Galactic Wolf-Rayet Stars

Most of the Milky Way's evolved massive stellar population is hidden from view. We can attempt to remedy this situation with near-infrared observations, and in this paper we present our method for detecting Wolf-Rayet stars in highly extincted regions and apply it to the inner Galaxy. Using narrow band filters at K-band wavelengths, we demonstrate how WR stars can be detected in regions where they are optically obscured. Candidates are selected for spectroscopic follow-up from our relative line and continuum photometry. The final results of applying this method with a NIR survey in the Galactic plane will provide a more complete knowledge of the structure of the galactic disk, the role of metallicity in massive stellar evolution, and environments of massive star formation. In this paper we briefly describe the survey set-up and report on recent progress. We have discovered four emission-line objects in the inner Galaxy: two with nebular emission lines, and two new WR stars, both of late WC subtype.

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arXiv2001

The CHANDRA HETGS X-ray Grating Spectrum of Eta Car

Eta Car may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. The CHANDRA X-ray observatory has obtained a calibrated, high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emisssion. Our 89 ksec CHANDRA observation with the High Energy Transmission Grating Spectrometer (HETGS) shows that the hot gas near the star is non-isothermal. The temperature distribution may represent the emission on either side of the colliding wind bow shock, effectively ``resolving'' the shock. If so, the pre-shock wind velocities are ~ 700 and ~ 1800 km/s in our analysis, and these velocities may be interpreted as the terminal velocities of the winds from Eta Car and from the hidden companion star. The forbidden-to-intercombination (f/i) line ratios for the He-like ions of S, Si and Fe are large, indicating that the line forming region lies far from the stellar photosphere. The iron fluorescent line at 1.93 Angstrom, first detected by ASCA, is clearly resolved from the thermal iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in our CHANDRA observation than in any of the ASCA spectra. The CHANDRA observation also provides an uninterrupted high-time resolution lightcurve of the stellar X-ray emission from Eta Car and suggests that there was no significant, coherent variability during the CHANDRA observation. The Eta Car CHANDRA grating spectrum is unlike recently published X-ray grating spectra of single massive stars in significant ways and is generally consistent with colliding wind emission in a massive binary.

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arXiv2001

The Stellar Content of Obscured Galactic Giant H II Regions III.: W31

We present near infrared (J, H, and K) photometry and moderate resolution (lambda/Deltalambda = 3000) K-band spectroscopy of the embedded stellar cluster in the giant H II region W31. Four of the brightest five cluster members are early O--type stars based on their spectra. We derive a spectro--photometric distance for W31 of 3.4 +/- 0.3 kpc using these new spectral types and infrared photometry. The brightest cluster source at K is a red object which lies in the region of the J - H vs. H - K color--color plot inhabited by stars with excess emission in the K-band. This point source has an H plus K-band spectrum which shows no photospheric features, which we interpret as being the result of veiling by local dust emission. Strong Brackett series emission and permitted FeII emission are detected in this source; the latter feature is suggestive of a dense inflow or outflow. The near infrared position of this red source is consistent with the position of a 5 GHz thermal radio source seen in previous high angular resolution VLA images. We also identify several other K-band sources containing excess emission with compact radio sources. These objects may represent stars in the W31 cluster still embedded in their birth cocoons.

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arXiv2000

The Stellar Content of Obscured Galactic Giant H II Regions: II. W42

We present near infrared J, H, and K images and K-band spectroscopy in the giant HII region W42. A massive star cluster is revealed; the color-color plot and K-band spectroscopic morphology of two of the brighter objects suggest the presence of young stellar objects. The spectrum of the bright central star is similar to unobscured stars with MK spectral types of O5-O6.5. If this star is on the zero age main sequence, then the derived spectrophotometric distance is considerably smaller than previous estimates. The Lyman continuum luminosity of the cluster is a few times that of the Trapezium. The slope of the K-band luminosity function is similar to that for the Trapezium cluster and significantly steeper than that for the massive star cluster in M17 or the Arches cluster near the Galactic center.

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arXiv1998

The Stellar Content of Obscured Galactic Giant H II Regions

Near infrared images of the Galactic giant HII region W43 reveal a dense stellar cluster at its center. Broad band JHK photometry of the young cluster and K-band spectra of three of its bright stars are presented. The 2 micron spectrum of the brightest star in the cluster is very well matched to the spectra of Wolf-Rayet stars of sub-type WN7. Two other stars are identified as O type giants or supergiants by their NIII and CIV emission. The close spatial clustering of O and the hydrogen WN type stars is analogous to the intense star burst clusters R136 in the Large Magellanic Cloud and NGC3603 in the Galaxy.

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arXiv1998

2 um Narrow-Band Imaging of the Sagittarius D H II region

We present 2 um narrow-band images of the core H II region in the Galactic star forming region Sagittarius D. The emission-line images are centered on 2.17 um (Brgamma) and 2.06 um (He I). The H II region appears at the edge of a well defined dark cloud, and the morphology suggests a blister geometry as pointed out in earlier radio continuum work. There is a deficit of stars in general in front of the associated dark cloud indicating the H II region is located in-between the Galactic center and the sun. The lesser spatial extent of the He I line emission relative to Brgamma places the effective temperature of the ionizing radiation field below 40,000 K. The He I 2.06 um to Brgamma ratio and Brgamma / far infrared dust emission put Teff at about 36,500 K to 40,000 K as derived from ionization models.

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