arXiv subjects

R. D. Blum

Publications and source records attributed to R. D. Blum.

27 records · Page 2Linked to original sources

arXiv2002

Optical and Infrared Spectroscopy of SN 1999ee and SN 1999ex

We report optical and infrared spectroscopic observations of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both of which were hosted by the galaxy IC 5179. For SN 1999ee we obtained a continuous sequence with an unprecedented wavelength and temporal coverage beginning 9 days before maximum light and extending through day 42. Before maximum light SN 1999ee displayed a normal spectrum with a strong Si II 6355 absorption, thus showing that not all slow-declining SNe are spectroscopically peculiar at these evolutionary phases. A comparative study of the infrared spectra of SN 1999ee and other Type Ia supernovae shows that there is a remarkable homogeneity among the Branch-normal SNe Ia during their first 60 days of evolution. SN 1991bg-like objects, on the other hand, display spectroscopic peculiarities at infrared wavelengths. SN 1999ex was characterized by the lack of hydrogen lines, weak optical He I lines, and strong He I 10830,20581, thus providing an example of an intermediate case between pure Ib and Ic supernovae. We conclude therefore that SN 1999ex provides first clear evidence for a link between the Ib and Ic classes and that there is a continuous spectroscopic sequence ranging from the He deficient SNe Ic to the SNe Ib which are characterized by strong optical He I lines.

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arXiv2001

2 um Narrow-band Adaptive Optics Imaging in the Arches Cluster

Canada-France-Hawaii-Telescope adaptive optics bonnette images through narrow-band filters in the $K-$band are presented for the Arches cluster. Continuum fluxes, line fluxes, and equivalent widths are derived from high angular resolution images, some near diffraction limited, for the well known massive stars in the Arches cluster. Images were obtained in the lines of \ion{He}{1} 2.06 \mic, \ion{H}{1} Br$γ$ (2.17 \mic), and \ion{He}{2} 2.19 \mic as well as continuum positions at 2.03 \mic, 2.14 \mic, and 2.26 \mic. In addition, fluxes are presented for \ion{H}{1} P$α$ (1.87 \mic) and a nearby continuum position (1.90 \mic) from Hubble Space Telescope archival data. The 2 \mic and P$α$ data reveal two new emission-line stars and three fainter candidate emission-line objects. Indications for a spectral change of one object between earlier observations in 1992/1993 and our data from 1999 are found. The ratio of \ion{He}{2} 2.19 \mic to Br$γ$ emission exhibits a narrow distribution among the stars, suggesting a narrow evolutionary spread centered predominantly on spectral types O4 If or Wolf-Rayet stars of the WN7 sub-type. From the approximate spectral types of the identified emission-line stars and comparisons with evolutionary models we infer a cluster age between $\sim$ 2 and 4.5 Myr.

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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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arXiv1997

H-Band Spectroscopic Classification of OB Stars

We present a new spectroscopic classification for OB stars based on H-band (1.5 micron to 1.8 micron) observations of a sample of stars with optical spectral types. Our initial sample of nine stars demonstrates that the combination of He I 1.7002 micron and H Brackett series absorption can be used to determine spectral types for stars between about O4 and B7 (to within about +/- 2 sub-types). We find that the Brackett series exhibits luminosity effects similar to the Balmer series for the B stars. This classification scheme will be useful in studies of optically obscured high mass star forming regions. In addition, we present spectra for the OB stars near 1.1 micron and 1.3 micron which may be of use in analyzing their atmospheres and winds.

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arXiv1996

Really Cool Stars at the Galactic Center

New and existing K-band spectra for 19 Galactic center late-type stars have been analyzed along with representative spectra of disk and bulge M giants and supergiants. Absorption strengths for strong atomic and molecular features have been measured. The Galactic center stars generally exhibit stronger absorption features centered near Na I (2.206 mic) and Ca I (2.264 mic) than representative disk M stars at the same CO absorption strength. Based on the absolute K-band magnitudes and CO and H2O absorption strengths for the Galactic center stars and known M supergiants and asymptotic giant branch (AGB) stars, we conclude that only IRS 7 must be a supergiant. Two other bright stars in our Galactic center sample are likely supergiants as well. The remaining bright, cool stars in the Galactic center that we have observed are most consistent with being intermediate mass/age AGB stars. We identify four of the Galactic center stars as long period variables based on their K-band spectral properties and associated photometric variability. Estimates of initial masses and ages for the GC stars suggest multiple epochs of star formation have occurred in the Galactic center over the last 7-100 Myr.

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arXiv1996

JHKL Photometry and the K-band Luminosity Function at the Galactic Center

J, H, K, and L photometry for the stars in the central 2' (5 pc) of the Galaxy are presented. Using the observed J-H, H-K, and K-L colors and assumed intrinsic colors, we determine the interstellar extinction at 2.2 mic (A_K) for approximately 1100 individual stars. The mean A_K (= 3.3 mag) is similar to previous results, but we find that the reddening is highly variable and some stars are likely to be seen through A_K > 6 mag. The de-reddened K-band luminosity function points to a significantly brighter component to the stellar population (> 1.5 mag at K) than found in the stellar population in Baade's window, confirming previous work done at lower spatial resolution. The observed flux of all Galactic center stars with estimated Ko (de-reddened magnitude) </= 7.0 mag is approx 25 % of the total in the 2' X 2' field. Our observations confirm the recent finding that several bright M stars in the Galactic center are variable. Our photometry also establishes the near-infrared variability of the M1-2 supergiant, IRS 7.

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