Outer Bulge Research Articles

Results from a Survey of Gravitational Microlensing toward M31

We describe the results of a search for microlensing events affecting stars in the outer bulge and inner disk of M31, due both to masses in M31 and the Galaxy. These observations, from 1994 and 1995 on the Vatican Advanced Technology Telescope and KPNO 4 m telescope, are sufficient to rule out masses in the range ~0.003-0.08 M☉ as the primary constituents of the mass of M31 toward this field. Furthermore, we find six candidate events consistent with microlensing as a result of masses of about 1 M☉, but we suspect that some of these may be cases in which long-period red supergiant variables may be mistaken for microlensing events. Coverage from anticipated data should be helpful in determining whether these sources maintain a constant baseline, and therefore they are best described by microlensing events.

Near-Infrared Structure of the Edge-on Spiral NGC 4565

view Abstract Citations (17) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Structure of the Edge-on Spiral NGC 4565 Rice, W. ; Merrill, K. Michael ; Gatley, Ian ; Gillett, F. C. Abstract Near-infrared J, H, and K band images of the edge-on Sb spiral NGC 4565 are analyzed to investigate the underlying stellar structure of the galaxy. The integrated near-infrared magnitudes of the galaxy and the "intrinsic" (J - K) and (H - K) colors of the disk and bulge outside the NGC 4565 dust lane are reported. The 2.2 micron K-light surface brightness distribution of the NGC 4565 disk and bulge are modeled. The disk is fit to a decaying exponential along the radial direction and a hyperbolic secant function along the vertical (z-height) direction. The bulge brightness profile along the minor axis cannot be adequately modeled with the most popular bulge fitting laws or with an exponential as proposed by Frankston & Schild [AJ, 81,500 (1976)]. We use a combination of an r^1/4^ law for the bulge core and an exponential for the outer bulge to model the bulge. The azimuthal brightness distribution of the bulge is modeled with a "boxy" ellipsoid. The residual near- infrared absorption and emission features of NGC 4565 after removal of the model galaxy are examined. Within the NGC 4565 dust lane E(J- K) increases with the depth of the dust extinction. The K-light optical depth derived for the densest regions of the dust lane (τ_K_ = 0.40) is similar to that found by Rix & Rieke [ApJ, 418, 123(1993)] for the dust lanes of M51. Estimates of the scale length and scale height of the dust lane are reported. Based on a comparison of the radial profile of the residual K-light emission of the NGC 4565 disk to constructed "edge- on profiles'' of the face-on galaxy M100 we propose a possible face-on appearance for the edge-on galaxy. Publication: The Astronomical Journal Pub Date: July 1996 DOI: 10.1086/117993 Bibcode: 1996AJ....112..114R Keywords: GALAXIES: SPIRAL; GALAXIES: INDIVIDUAL: NGC 4565; INFRARED: GALAXIES full text sources ADS | data products SIMBAD (4) NED (1)

Mass-losing stars in the South Galactic Cap

Observations are presented for 162 late-type stars in the South Galactic Cap (b < -30°) which were selected on the basis of their IRAS 25/12-µm flux ratios as high-mass-loss candidates. JHKL photometry (over 1100 observations) was obtained for all of the stars, BV(RI)C photometry for 78 of them and optical spectra for 51.154 of these stars are non-Mira M or S stars, of which many, and possibly all, are semi-regular variables. Of the remaining eight IRAS objects, three are T Tauri stars, three are interacting binaries and two are carbon stars. A few of the M giants and both of the carbon stars have circumstellar envelopes of the type more normally associated with Mira variables. These include two 1612-MHz OH maser sources. It is suggested that such stars may have been Miras in the recent past, but are currently out of the instability strip owing to a recently experienced helium-shell flash. Alternatively, some of them could be binary stars, but there is as yet no evidence for the second star. The near-infrared colours of the M giants are compared with those of similar stars in the Bulge. They are similar to those of the inner Bulge and unlike those found in either the outer Bulge or the globular clusters. The kinematics and Galactic distribution of the M giants indicate that they are probably from a mixed population and that they could be associated with Miras with a range of periods. A comparison of the observed colours with those derived from models indicates a range of metallicity with the bulk of stars slightly more metal-rich than the Sun. It also reveals significant numbers of stars with colours outside the predicted range, possible due to the effects of circumstellar reddening or to inadequacies in the models. The most metal-rich examples of the M stars have high mass-loss rates for non-Miras |$(\sim 10^{-6}\enspace \text M_\odot\enspace \text {yr}^{-1})$| and there are far fewer of them outside than inside the solar circle. This may be due to a metallicity gradient. These stars have a scaleheight of more than 500 pc. The two carbon stars have unusual colours and detached shells. One of them, R Scl, is shown to vary with a period of 379 d superimposed on a possible second period of about 2300 d. The other carbon star, which is more distant and previously unknown, may also have double-period variations.

Infrared speckle observations of the nucleus of M31

view Abstract Citations (4) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Speckle Observations of the Nucleus of M31 Spillar, E. J. ; Canterna, R. ; Carels, K. H. ; Benson, J. A. ; Dyck, H. M. Abstract Two micron (K band), one-dimensional speckle observations of the center of M31 have been obtained with the Wyoming Infrared Observatory's 2.3 m telescope. Visibility curves have been produced and compared with a three-component model consisting of a nucleus, an inner bulge, and an outer bulge. The bulge model is based on Kent's r band surface brightness measurements. A variable size compact nuclear source is superposed on the inner bulge. The FWHM of the compact nuclear source from the model which best fits the data is 0.1" (a diameter of 0.35 pc), with a range of possible values from 0.5" FWHM (a diameter of 1.7 pc) to an unresolved point. From our best model we infer that the nuclear source contributes up to 11% of the K band flux within a 6.2" aperture centered on the nucleus. Combining the speckle data with K band photometry, we estimate the nuclear component to be K = 10.5 +/- 0.3. Combining this fact with the V band data from Kinman and Light et al., we find the V-K color is significantly bluer for the compact nuclear source (V-K = 2.1 +/- 0.4) than for the inner bulge (V-K = 3.6 +/- 0.2). Publication: The Astrophysical Journal Pub Date: January 1990 DOI: 10.1086/185639 Bibcode: 1990ApJ...349L..13S Keywords: Andromeda Galaxy; Galactic Nuclei; Infrared Astronomy; Speckle Interferometry; Astronomical Models; Brightness Distribution; Galactic Bulge; Galactic Structure; Infrared Spectroscopy; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M31; GALAXIES: NUCLEI; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (1) NED (1)