778 research outputs found
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, non-sinusoidal
photometric modulations are apparent, suggestive of superhumps, placing SDSS
J2100 in the SU UMa subclass of dwarf novae. However, the periods during
outburst and quiescence differ significantly, being 2.099 plus or minus 0.002
hr and 1.96 plus or minus 0.02 hr respectively. Our phase-resolved spectroscopy
during outburst yielded an estimate of about 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.Comment: 6 pages, 5 eps figures, accepted by PASP Dec. 16th, 200
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 lightcurves
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 line O VII (E=0.57 keV), 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 broad band curve. The X-ray spectra
require the presence of both hard and soft X-ray components, with their
luminosity ratio consistent with that found in other recent XMM-Newton results
on polars. Lastly, SDSS J170053.30+400357.6 appears optically as a very typical
polar, however its large amplitude optical modulation is 180 degrees out of
phase with the variation in our short X-ray lightcurve.Comment: 9 pages, 9 figures, accepted for publication in the ApJ (January
2005
Characterizing Three Candidate Magnetic CVs from SDSS: XMM-Newton and Optical Follow-up Observations
In the latest in our series of papers on XMM-Newton and ground-based optical
follow-up of new candidate magnetic cataclysmic variables (mCVs) found in the
Sloan Digital Sky Survey, we report classifications of three systems: SDSS
J144659.95+025330.3, SDSS J205017.84-053626.8, and SDSS J210131.26+105251.5.
Both the X-ray and optical fluxes of SDSS J1446+02 are modulated on a period of
48.7+/-0.5 min, with the X-ray modulation showing the characteristic energy
dependence of photo-electric absorption seen in many intermediate polars (IP).
A longer period modulation and radial velocity variation is also seen at a
period around 4 hrs, though neither dataset set is long enough to constrain
this longer, likely orbital, period well. SDSS J2050-05 appears to be an
example of the most highly magnetized class of mCV, a disk-less, stream-fed
polar. Its 1.57 hr orbital period is well-constrained via optical eclipse
timings; in the X-ray it shows both eclipses and an underlying strong, smooth
modulation. In this case, broadly phase-resolved spectral fits indicate that
this change in flux is the result of a varying normalization of the dominant
component (a 41 keV MEKAL), plus the addition of a partial covering absorber
during the lower flux interval. SDSS J2101+10 is a more perplexing system to
categorize: its X-ray and optical fluxes exhibit no large periodic modulations;
there are only barely detectable changes in the velocity structure of its
optical emission lines; the X-ray spectra require only absorption by the
interstellar medium; and the temperatures of the MEKAL fits are low, with
maximum temperature components of either 10 or 25 keV. We conclude that SDSS
J2101+10 can not be an IP, nor likely a polar, but is rather most likely a disc
accretor-- a low inclination SW Sex star.Comment: 12 pages, 9 figures, accepted for publication in the Astronomical
Journa
A Subsurface Eddy Associated With a Submarine Canyon Increases Availability and Delivery of Simulated Antarctic Krill to Penguin Foraging Regions
The distribution of marine zooplankton depends on both ocean currents and swimming behavior. Many zooplankton perform diel vertical migration (DVM) between the surface and subsurface, which can have different current regimes. If concentration mechanisms, such as fronts or eddies, are present in the subsurface, they may impact zooplankton near-surface distributions when they migrate to near-surface waters. A subsurface, retentive eddy within Palmer Deep Canyon (PDC), a submarine canyon along the West Antarctic Peninsula (WAP), retains diurnal vertically migrating zooplankton in previous model simulations. Here, we tested the hypothesis that the presence of the PDC and its associated subsurface eddy increases the availability and delivery of simulated Antarctic krill to nearby penguin foraging regions with model simulations over a single austral summer. We found that the availability and delivery rates of simulated krill to penguin foraging areas adjacent to PDC were greater when the PDC was present compared to when PDC was absent, and when DVM was deepest. These results suggest that the eddy has potential to enhance krill availability to upper trophic level predators and suggests that retention may play a significant role in resource availability for predators in other similar systems along the WAP and in other systems with sustained subsurface eddies
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