Oliver J. Fraser

Meeting the Cool Neighbors. VIII. A Preliminary 20 Parsec Census from the NLTT Catalogue

Continuing our census of late-type dwarfs in the solar neighborhood, we present BVRI photometry and optical spectroscopy of 800 mid-type M dwarfs drawn from the NLTT proper-motion catalog. The targets are taken both from our own cross-referencing of the NLTT Catalogue and the 2MASS Second Incremental Data Release, and from the revised NLTT compiled recently by Salim & Gould. All are identified as nearby-star candidates based on their location in the (mr, mrKs) diagram. Three hundred stars discussed here have previous astrometric, photometric, or spectroscopic observations. We present new BVRI photometry for 101 stars, together with low- resolution spectroscopy of a further 400 dwarfs. In total, we find that 241 stars are within 20 pc of the Sun, while a further 70 lie within 1 � of our distance limit. Combining the present results with previous analyses, we have quantitative observations for 1910 of the 1913 candidates in our NLTT nearby-star samples. Eight hundred fifteen of those stars have distance estimates of 20 pc or less, including 312 additions to the local census. With our NLTT follow-up observations essentially complete, we have searched the literature for K and early-type M dwarfs within the sampling volume covered by the 2MASS second release. Comparing the resultant 20 pc census against predicted numbers, derived from the 8 pc luminosity function, shows an overall deficit of � 20% for stellar systems and � 35% for individual stars. Almost all are likely to be fainter than MJ ¼ 7, and at least half are probably as yet undiscovered companions of known nearby stars. Our results suggest that there are relatively few missing systems at the lowest luminosities, MJ > 8:5. We discuss possible means of identifying the missing stars.

Cataclysmic Variables from the Sloan Digital Sky Survey. II. The Second Year

The first full year of operation following the commissioning year of the Sloan Digital Sky Survey has revealed a wide variety of newly discovered cataclysmic variables. We show the SDSS spectra of forty-two cataclysmic variables observed in 2002, of which thirty-five are new classifications, four are known dwarf novae (CT Hya, RZ Leo, T Leo and BZ UMa), one is a known CV identified from a previous quasar survey (Aqr1) and two are known ROSAT or FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS positions, colors and spectra of all forty-two systems are presented. In addition, the results of follow-up studies of several of these objects identify the orbital periods, velocity curves and polarization that provide the system geometry and accretion properties. While most of the SDSS discovered systems are faint (>18th mag) with low accretion rates (as implied from their spectral characteristics), there are also a few bright objects which may have escaped previous surveys due to changes in the mass transfer rate.The first full year of operation following the commissioning year of the Sloan Digital Sky Survey (SDSS) has revealed a wide variety of newly discovered cataclysmic variables (CVs). We show the SDSS spectra of 42 CVs observed in 2002, of which 35 are new classifications, four are known dwarf novae (CT Hya, RZ Leo, T Leo, and BZ UMa), one is a known CV identified from a previous quasar survey (Aqr1), and two are known ROSAT or FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS positions, colors, and spectra of all 42 systems are presented. In addition, the results of follow-up studies of several of these objects identify the orbital periods, velocity curves, and polarization that provide the system geometry and accretion properties. While most of the SDSS discovered systems are faint (greater than 18th magnitude) with low accretion rates (as implied from their spectral characteristics), there are also a few bright objects that may have escaped previous surveys due to changes in the mass transfer rate.

Cataclysmic variables from the Sloan Digital Sky Survey. III. The third year

Novel magnetic resonance imaging agents comprise complexes of paramagnetic ions with hydrazide derivatives of polyaminocarboxylic acid chelating agents. These novel imaging agents are characterized by excellent NMR image-contrasting properties and by high solubilities in physiological solutions. A novel method of performing an NMR diagnostic procedure involves administering to a warm-blooded animal an effective amount of a complex as described above and then exposing the warm-blooded animal to an NMR imaging procedure, thereby imaging at least a portion of the body of the warm-blooded animal.

THE PROPERTIES OF LONG-PERIOD VARIABLES IN THE LARGE MAGELLANIC CLOUD FROM MACHO

We present a new analysis of the long-period variables in the Large Magellanic Cloud (LMC) from the MACHO Variable Star Catalog. Three-quarters of our sample of evolved, variable stars have periodic light curves. We characterize the stars in our sample using the multiple periods found in their frequency spectra. Additionally, we use single-epoch Two Micron All Sky Survey measurements to construct the average infrared light curves for different groups of these stars. Comparison with evolutionary models shows that stars on the red giant branch (RGB) or the early asymptotic giant branch (AGB) often show non-periodic variability, but begin to pulsate with periods on the two shortest period-luminosity (P-L) sequences (3 & 4) when they brighten to K s ≈ 13. The stars on the thermally pulsing AGB are more likely to pulsate with longer periods that lie on the next two P-L sequences (1 & 2), including the sequence associated with the Miras in the LMC. The Petersen diagram and its variants show that multi-periodic stars on each pair of these sequences (3 & 4, and 1 & 2) typically pulsate with periods associated only with that pair. The periods in these multi-periodic stars become longer and stronger as the star evolves. We further constrain the mechanism behind the long secondary periods (LSPs) seen in half of our sample, and find that there is a close match between the luminosity functions of the LSP stars and all of the stars in our sample, and that these stars pulsation amplitudes are relatively wavelength independent. Although this is characteristic of stellar multiplicity, the large number of these variables is problematic for that explanation.

Meeting the Cool Neighbors. VII. Spectroscopy of Faint Red NLTT Dwarfs

We present low-resolution optical spectroscopy and BVRI photometry of 453 candidate nearby stars drawn from the NLTT proper-motion catalog. The stars were selected based on optical/near-infrared colors, derived by combining the NLTT photographic data with photometry from the 2MASS Second Incremental Data Release. Based on the derived photometric and spectroscopic parallaxes, we identify 111 stars as lying within 20 pc of the Sun, including nine stars with formal distance estimates of less than 10 pc. A further 53 stars have distance estimates within 1 ? of our 20 pc limit. Almost all of those stars are additions to the nearby-star census. In total, our NLTT-based survey has so far identified 496 stars likely to be within 20 pc, of which 195 are additions to nearby-star catalogs. Most of the newly identified nearby stars have spectral types between M4 and M8.

Long-Period Variables in the Large Magellanic Cloud: Results from MACHO and 2MASS

We use the 8 year light-curve database from the MAssive Compact Halo Objects project together with infrared colors and magnitudes from the Two Micron All Sky Survey to identify a sample of 22,000 long-period variables in the Large Magellanic Cloud (referred to hereafter as LMC LPVs). A period-luminosity diagram of these stars reveals six well-defined sequences, in substantial agreement with previous analyses of samples from the Optical Gravitational Lensing Experiment. In our analysis we identify analogues to Galactic LPVs in the LMC LPV sample. We find that carbon-dominated asymptotic giant branch (AGB) stars populate only two of the sequences, one of which includes the Mira variables. The high-luminosity end of the same two sequences are also the location of the only stars with J - Ks > 2, indicating that they are enshrouded in dust. The unknown mechanism that drives the variability of stars in the longest period produces different morphology in the period-luminosity diagram as compared with the shortest period sequences, which are thought to be caused by pulsation. In particular, the longest period sequence extends to lower luminosity red giant branch stars, and the luminosity function does not peak among the AGB stars. We point out several features that will constrain new models of the period-luminosity sequences.

Discovery of two new accreting pulsating white dwarf stars

We report the discovery of two new accreting pulsating white dwarf stars among the cataclysmic variables of the Sloan Digital Sky Survey: SDSS J074531.91+453829.5 and SDSS J091945.10+085710.0. We observe high-amplitude nonsinusoidal variations of 4.5%-7% at a period close to 1230 s in the optical light curves of SDSS J074531.91+453829.5 and a low-amplitude variation of 0.7%-1.6% near 260 s in the light curves of SDSS J091945.10+085710.0. We infer that these optical variations are a consequence of nonradial g-mode pulsations in the accreting primary white dwarfs of these cataclysmic variables. However, we cannot rule out the remote possibility that the 260 s period could be the spin period of the accreting white dwarf SDSS J091945.10+085710.0. We also uncovered a nonvariable, SDSS J171145.08+301320.0, during our search; our two observing runs exclude any pulsation-related periodicities in the range 85-1400 s with an amplitude >= 0.5%. This discovery paper brings the total number of known accreting white dwarf pulsators to 11.

Planetary Nebula Central Stars and Symbiotic Stars in the MACHO Galactic Bulge Database

We have examined central stars of planetary nebulae and symbiotic stars found in the MACHO Galactic bulge database to look for variability. We found four central stars of planetary nebulae and eight symbiotic stars that show variability. We examine thevariability and the nature of these objects in detail, as well as reporting on the objects that we did not find to be variable. catalogs 1 and the full database of detected sources. Sources from the full MACHO database of millions of objects were selected for the MGB Variable Star Catalog if the central 80% of points in the objects light curve failed to fit a constant magnitude in a χ-square test. This criterion resulted in 521,007 candidate variables in the Galactic bulge. 2 MACHO data were taken simultaneously in two nonstandard filters: red and blue. These can be transformed to Cousins V and R using the method of Bessell & Germany (1999), which was calibrated for metal-poor giants. We present these magnitudes here in the interest of providing rough estimates. When we only have data in one MACHO band, we assume a color of 0 for PNCS and 1 for SS

SDSS J210014.12+004446.0: A New Dwarf Nova with Quiescent Superhumps?*

We report follow-up observations of the Sloan Digital Sky Survey cataclysmic variable SDSS J210014.12+004446.0 (hereafter SDSS J2100). We obtained photometry and spectroscopy in both outburst and quiescent states, providing the first quiescent spectrum of this source. In both states, nonsinusoidal photometric modulations suggestive of superhumps are apparent, placing SDSS J2100 in the SU UMa subclass of dwarf novae. However, the periods during outburst and quiescence differ significantly, at 2.099±0.002 and 1.96±0.02 hr, respectively. Our phase-resolved spectroscopy during outburst yielded an estimate of ~2 hr for the orbital period, consistent with the photometry. The presence of the shorter period modulation at quiescence is unusual, but not unique. Another atypical feature is the relative weakness of the Balmer emission lines in quiescence. Overall, we find a close similarity between SDSS J2100 and the well-studied superhump cataclysmic variable V503 Cygni. By analogy, we suggest that the quiescent modulation is due to a tilted accretion disk—producing negative superhumps—and the modulation in outburst is due to positive superhumps from the precession of an elliptical disk.

XMM-Newton and Optical Follow-up Observations of Three New Polars from the Sloan Digital Sky Survey* **

We report follow-up XMM-Newton and optical observations of three new polars found in the Sloan Digital Sky Survey. Simple modeling of the X-ray spectra, and consideration of the details of the X-ray and optical light curves corroborate the polar nature of these three systems and provide further insights into their accretion characteristics. During the XMM-Newton observation of SDSS J072910.68+365838.3, X-rays are undetected apart from a probable flare event, during which we find both the typical hard X-ray bremsstrahlung component and a very strong O VII (E = 0.57 keV) line, but no evidence of a soft blackbody contribution. In SDSS J075240.45+362823.2 we identify an X-ray eclipse at the beginning of the observation, roughly in phase with the primary minimum of the optical broadband curve. The X-ray spectra require the presence of both hard and soft X-ray components, in a luminosity ratio consistent with that found in other recent XMM-Newton results on polars. SDSS J170053.30+400357.6 appears optically as a very typical polar; however, its large-amplitude optical modulation is 180° out of phase with the variation in our short X-ray light curve.