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Luminosity-velocity diagrams for 12 spiral galaxies in the Virgo cluster are presented. Optical rotation curves obtained for the innermost portions of eight galaxies, complemented with velocity data from the literature, are coupled with luminosity growth curves to investigate the distance indication capabilities of the initial linear branch (ILB) feature and to delve into the physical basis for the T-F relation. Luminosity growth curves are obtained from Gunn r CCD images. The ILB feature is found to have a substantially larger dispersion in slope (~0.9) (and consequently, zero point) than previously thought. Plotting the magnitude and velocity of the final point in the ILB for all the galaxies in our sample yields a tight correlation (essentially an "inner T-F relation"), with the caveat that two galaxies are rejected from the fit (one is foreground, the other is a member of a binary pair). Ramifications of this relation are briefly discussed. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

We present a detailed analysis of the white dwarf luminosity functions derived from the local 40 pc sample and the deep proper motion catalog of Munn et al. Many previous studies have ignored the contribution of thick disk white dwarfs to the Galactic disk luminosity function, which results in an erroneous age measurement. We demonstrate that the ratio of thick/thin disk white dwarfs is roughly 20% in the local sample. Simultaneously fitting for both disk components, we derive ages of 6.8-7.0 Gyr for the thin disk and 8.7 +/- 0.1 Gyr for the thick disk from the local 40 pc sample. Similarly, we derive ages of 7.4-8.2 Gyr for the thin disk and 9.5-9.9 Gyr for the thick disk from the deep proper motion catalog, which shows no evidence of a deviation from a constant star formation rate in the past 2.5 Gyr. We constrain the time difference between the onset of star formation in the thin disk and the thick disk to be 1.6(-0.4)(+0.3) Gyr. The faint end of the luminosity function for the halo white dwarfs is less constrained, resulting in an age estimate of 12.5(-3.4)(+1.4) Gyr for the Galactic inner halo. This is the first time that ages for all three major components of the Galaxy have been obtained from a sample of field white dwarfs that is large enough to contain significant numbers of disk and halo objects. The resultant ages agree reasonably well with the age estimates for the oldest open and globular clusters.

A catalog of 8472 white dwarf (WD) candidates is presented, selected using reduced proper motions from the deep proper motion catalog of Munn et al. Candidates are selected in the magnitude range 16 < r < 21.5 over 980 square degrees, and 16 < r < 21.3 over an additional 1276 square degrees, within the Sloan Digital Sky Survey (SDSS) imaging footprint. Distances, bolometric luminosities, and atmospheric compositions are derived by fitting SDSS ugriz photometry to pure hydrogen and helium model atmospheres (assuming surface gravities log g = 8). The disk white dwarf luminosity function (WDLF) is constructed using a sample of 2839 stars with 5.5 < M-bol < 17, with statistically significant numbers of stars cooler than the turnover in the luminosity function. The WDLF for the halo is also constructed, using a sample of 135 halo WDs with 5 < M-bol < 16. We find space densities of disk and halo WDs in the solar neighborhood of 5.5 +/- 0.1 x 10(-3) pc(-3) and 3.5 +/- 0.7 x 10(-5) pc(-3), respectively. We resolve the bump in the disk WDLF due to the onset of fully convective envelopes in WDs, and see indications of it in the halo WDLF as well.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 106-112). / Microfiche. / x, 112 leaves, bound ill. (some col.) 29 cm

I analyse an x-ray selected sample of 128 late-type (F-M) stars. These stars were identified as optical counterparts to serendipitous x-ray detections made by the Einstein Observatory Extended Medium Sensitivity Survey. Once identified as x-ray sources, the stars were reobserved with an extensive program of optical observations consisting of high- and low-resolution spectroscopy and photometry. Spectral types, luminosity classes, absolute magnitudes, distances, x-ray luminosities, projected rotation rates (v sin i), radial velocities, and binary status have been determined for the sample. I find that Lₓ is correlated with v sin i for single stars. However, Lₓ does not correlate with Ω sin i, which leads me to believe that the correlation seen with v sin i is actually a correlation with radius. Indeed, Lₓ correlates strongly with radius (color, mass) for main sequence stars. This result provides a plausibility argument for rotational saturation in the coronae of late-type stars. Since this sample is flux limited, I use sky coverage and sensitivity information from the Einstein Observatory to calculate the bright end of the x-ray luminosity function for late-type stars. It appears that previously calculated luminosity functions from optically selected samples have underestimated the number of x-ray bright F and G dwarfs. I have also discovered 8 previously uncatalogued M dwarfs within 25 pc of the sun. My sample includes only M dwarfs of spectral type M5 and earlier, 93% of which are "emission" stars (i.e. type Me V), as well as two pre-main sequence M stars. Arguments involving kinematics and stellar rotational velocities are used to estimate the age of these x-ray "bright" M dwarfs; they appear to be quite young (≤ 1-3 x 10⁹ yrs). Since the local space density of x-ray "bright" M dwarfs increases with mass, I infer a longer activity timescale for lower masses. M dwarfs later than M5 lie below the sample's x-ray sensitivity limit. An upper limit of log Lₓ = 27.45 is put on their coronal emission. I also present H(α) and Ca II K line fluxes for most members of the M dwarf sample and show that the H(α) and Ca II K luminosities do indeed correlate with Lₓ. However, these chromospheric luminosities are weaker functions of rotation than Lₓ and may, in fact, represent saturated levels of activity. My results are consistent with the hypothesis that the chromosphere is heated by x-rays from the overlying corona. Finally, I discuss two unusual members of the sample which are attractive candidates for the recently proposed class of FK Comae stars.

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Study determined if 2MASS photometric data are reliable for luminosity classification using JHK plots of Reid and Hawley (2001). Effects of interstellar reddening on the placement of giant and dwarf data on the JIIK plot were analyzed. Dwarfs (N=54) were selected from Hipparchos and the 2MASS data reduced to an H-K range of 0.14-0.40. A disk dwarf region was identified using linear regression on the low space velocity stars. Giants selected from Volume 5 of the Michigan Catalogue of HD stars and SAG stars classified at Ball State University. They yielded 304 individual giants and 13 matches in the 0.14-0.40 H-K range respectively. The 2MASS data was reliable for luminosity classification of the SAGBSU giants. The classification of the Michigan giants was not possible due to interstellar reddening and the likely presence of faint giant companions. / Department of Physics and Astronomy

This paper presents the photometric luminosity classification of M dwarfs in Kaptyn’s Selected Area 124 (SA124). This project is part of an ongoing program at Ball State University to use R, I, and CaH photometry in an attempt to probe low luminosity star contributions to the luminosity function. Data is taken at the Southeastern Association for Research in Astronomy (SARA) telescope located at Kitt Peak, Arizona. With a limiting magnitude of R=15.0, we have observed ~75% of a full square degree in SA124 and have detected 19 M dwarf candidates, which are then confirmed using matched 2MASS J, H, and K magnitudes. We present the detections of 19 ±4.4 M dwarfs observed in SA124. The current estimates of our luminosity function are consistent with those previously determined for the galactic plane. / Department of Physics and Astronomy