By observing the high Galactic latitude equatorial sky in drift-scan mode with the QUEST (Quasar Equatorial Survey Team) Phase 1 camera, we have collected multibandpass photometry on a large strip of ...sky, resolved over a large range of timescales (from hourly to biennially). A robust method of ensemble photometry reveals those objects within the scan region that fluctuate in brightness at a statistically significant level. Subsequent spectroscopic observations of a subset of those varying objects easily discriminated the quasars from stars. For a 13 month time span, 38% of the previously known quasars within the scan region were seen to vary in brightness, and subsequent spectroscopic observation revealed that similar to 7% of all variable objects in the scan region are quasars. Increasing the time baseline to 26 months increased the percentage of previously known quasars that vary to 61% and confirms via spectroscopy that 7% of the variable objects in the region are quasars. This reinforces previously published trends and encourages additional and ongoing synoptic searches for new quasars and their subsequent analysis. During two spectroscopic observing campaigns, a total of 30 quasars were confirmed, 11 of which are new discoveries and 19 of which were determined to be previously known. Using the previously cataloged quasars as a benchmark, we find we can better optimize future variability surveys. This paper reports on the subset of variable objects that are spectroscopically confirmed as quasars.
This paper reports an update to the QUEST1 (QUasar Equatorial Survey Team, Phase 1) Variability Survey (QVS) light curve catalog, which links QVS instrumental magnitude light curves to Sloan Digital ...Sky Survey (SDSS) objects and photometry. In the time since the original QVS catalog release, the overlap between publicly available SDSS data and QVS data has increased by 8% in sky coverage and 16,728 in number of matched objects. The astrometric matching and the treatment of SDSS masks have been refined for the updated catalog. We report on these improvements and present multiple bandpass light curves, global variability information, and matched SDSS photometry for 214,941 QUEST1 objects.
The gray wolf is a large, highly mobile predator whose original geographic range included most of the Northern Hemisphere. High rates of genetic exchange probably characterized even ...distantly-separated populations in the past, but recent population declines and habitat fragmentation have isolated previously contiguous populations, especially in the Old World. We examine mitochondrial DNA (mtDNA) variability among twenty-six populations of wolves from throughout their geographic range. We find eighteen mtDNA genotypes in gray wolves: seven of these are derived from hybridization with coyotes, four are confined to the New World, six are confined to the Old World, and one is shared by both areas. Genetic differentiation among wolf populations is significant but small in magnitude. In the Old World, most localities have a single unique genotype, whereas in the New World several genotypes occur at most localities and three of the five genotypes are nearly ubiquitous. The pattern of genetic differentiation in the gray wolf contrasts with that of another large, highly vagile canid, the coyote, in which genetic differentiation among populations is not significant even among widely separated localities. We suggest that the difference between these two species reflects the rapid, recent increase in coyote numbers and expansion of their geographic range, and the coincident decline in gray wolf populations. Apparent genetic differences among extant wolf populations may be a recent phenomenon reflecting population declines and habitat fragmentation rather than a long history of genetic isolation.
Outbursts averaging 0.6 mag in amplitude and 10 d in width are described in five old novae and nova-like cataclysmic variables: UU Aqr, Q Cyg, CP Lac, X Ser, and RW Sex. These stars are thought to be ...high mass transfer rate systems for which the accretion disk is expected to be stable against the thermal instability responsible for dwarf nova outbursts. The widths and spacings of these events are similar to those of dwarf nova eruptions, but the amplitudes are significantly smaller, or 'stunted'. The outbursts are sometimes accompanied by dips. These dips have amplitudes that are similar to the outbursts, but have shapes that scatter significantly more than the shapes of the outbursts. The outbursts and dips sometimes occur as pairs and are sometimes isolated. We characterize these phenomena with regard to outburst shapes and frequency of occurrence and explore a range of possible causes, including truncated disks, mass transfer modulations, and Z Camelopardalis type behavior. Arguments are assembled for and against such possible mechanisms, and key observations are suggested. It appears unlikely that accretion disk instabilities are the single common cause of these phenomena, and we are left with either a combination of accretion disk and mass transfer events or a situation in which mass transfer events are somehow responsible for all these varied behaviors. (Author)
Images of comet C/1996 B2 (Hyakutake) taken during its close approach to Earth show differences in the distribution of gas and dust in the inner coma and reveal two arc-shaped molecular resonant ...emission features. The morphology of these features, as well as the apparent decoupling gas from dust in the inner coma, suggest that an extended region of icy grains surrounds the nucleus of Hyakutake and contributes substantially to the production of volatiles. Model simulations suggest the same conclusion and indicate that the brighter arc is explainable by the presence of a trailing condensation of ice-bearing granules with a rate of volatile production approximately 23 percent of that of the nucleus.
We present extensive spectroscopy and photometry of the dwarf nova V630 Cassiopeiae. A late-type (K4–5) absorption spectrum is easily detectable, from which we derive the orbital parameters. We find ...a spectroscopic period of P=2.56387±4×10−5d and a semi-amplitude of K2=132.9±4.0 km s−1. The resulting mass function, which is a firm lower limit on the mass of the white dwarf, is then f(M)=0.624±0.056 M⊙. The secondary star is a ‘stripped giant’ and, using relations between the core mass and the luminosity and between the core mass and the radius, we derive a lower limit of M2.°0.165 M⊙ for the secondary star. The rotational velocity of the secondary star is not resolved in our spectra and we place a limit of Vrotsini<40kms−1. The long-term light curve shows variations of up to 0.4 mag on short (1–5 d) time-scales, and variations of 0.2–0.4 mag on longer (3–9 months) time-scales. In spite of these variations, the ellipsoidal light curve of the secondary star is easily seen when the data are folded on the spectroscopic ephemeris. Ellipsoidal models fitted to the mean light curve give an inclination in the range 66.°96.°i.°78.°08 (90 per cent confidence). This inclination range, and the requirement that M2.°0.165 M⊙ and Vrotsini<40kms−1, yields a white dwarf mass of M1=0.977−0.098+0.168M⊙ and a secondary star mass of M2=0.172−0.012+0.029M⊙ (90 per cent confidence limits). Our findings confirm the suggestion of Warner that V630 Cas is a rare example of a dwarf nova with a long orbital period.
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