723 research outputs found
Spectrophotometery of Brackett lines in very luminous IRAS galaxies
Observation of the Brackett-alpha and Brackett-gamma hydrogen recombination lines were made in a sample of galaxies chosen from the IRAS catalog to have high luminosities at infrared wavelengths. Most have strong Brackett line emission indicating large numbers of high mass stars; the formation of these stars may hence be the underlying source for the galaxies' luminosities. However, there are at least two exceptions that may not be explained in this manner: NGC 6240 and Arp 220. Additional evidence indicates that each of these exceptions may be more closely related to Seyfert-type galaxies or other active galactic nuclei
Luminosity Function of the Perigalactocentric Region
We present H and K photometry of 42,000 stars in an area of 250 arcmin
centered on the Galactic center. We use the photometry to construct a
dereddened K band luminosity function (LF) for this region, excluding the
excessively crowded inner 2' of the Galaxy. This LF is intermediate between the
LF of Baade's window and the LF of inner 2' of the Galactic center. We
speculate that the bright stars in this region have an age which is
intermediate between the starburst population in the Galactic center and the
old bulge population. We present the coordinates and mags for 16 stars with
K_{0} < 5 for spectroscopic follow up.Comment: 25 pages. Tarred, gzipped and uuencoded. Includes LaTex source file,
Figures 3 to 9 and 5 Tables. Figures 1 and 2 are available at
ftp://bessel.mps.ohio-state.edu/pub/vijay . Submitted to Ap
The Nature of the Variable Galactic Center Source IRS16SW
We report measurements of the light curve of the variable Galactic Center
source IRS16SW. The light curve is not consistent with an eclipsing binary or
any other obvious variable star. The source may be an example of a high mass
variable predicted theoretically but not observed previously.Comment: 11 pages, 2 figures. Accepted by Ap
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.Comment: Accepted by AJ. 37 pages (latex, aastex v4.0, 2 planotables, 5
figures, embedded, eps). Postscript also available at
ftp://degobah.colorado.edu/pub/rblum/RCS2, Some minor changes made to text
and figures regarding Stars IRS 28, OSUC1-3. No significant changes to
conclusion
Metallicity of Red Giants in the Galactic Bulge from Near-Infrared Spectroscopy
We present K-band spectra of more than 110 M giants in Galactic bulge fields
interior to -4 degrees and as close as 0.2 degrees of the Galactic Center. From
the equivalent widths of three features in these spectra, EW(Na),EW(Ca), and
EW(CO) we calculate [Fe/H] for the stars with a calibration derived from
globular clusters Stephens et al (2000). The mean [Fe/H] for each field is in
good agreement with the results from Frogel et al. (1999) based on the slope of
the giant branch method. We find no evidence for a metallicity gradient along
the minor or major axes of the inner bulge (R < 0.6 kpc). A metallicity
gradient along the minor axis, found earlier, arises when fields located at
larger galactic radius are included. However, these more distant fields are
located outside of the infrared bulge defined by the COBE/DIRBE observations.
We compute the [Fe/H] distribution for the inner bulge and find a mean value of
-0.21 dex with a full width dispersion of 0.30 dex, close to the values found
for Baade's Window (BW) by Sadler et al. (1996) and to a theoretical prediction
for a bulge formed by dissipative collapse Molla et al (2000).Comment: 32 pages, 10 figures, AJ submitte
- …