1,685 research outputs found
Spitzer Space Telescope Observations of Circumbinary Dust Disks around Polars
We present Spitzer Space Telescope IRAC photometry of the magnetic cataclysmic variables EF Eri, MR Ser, VV Pup, V834 Cen, GG Leo and V347 Pav. When we combine our results with the 2MASS data, we find that at least five of the polars have flux densities in the mid-IR in excess of the emission expected from the stellar components alone. We are unable to model this mid-IR excess with cyclotron emission, but we can recreate the observed spectral energy distributions with the inclusion of a simple circumbinary dust disk model. Importantly, we find that the masses of our modelled disks are approximately 12 orders of magnitude lower than required to significantly affect CV evolution. The accretion disk-less polars are ideal places to search for these disks, since the luminous accretion disk in most CVs would drown out the faint IR signature of the cooler, dimmer circumbinary disks
Spitzer 24-micron Time-Series Observations of the Eclipsing M-dwarf Binary GU Bootis
We present a set of {\it Spitzer} 24m MIPS time series observations of
the M-dwarf eclipsing binary star GU Bo\"otis. Our data cover three secondary
eclipses of the system: two consecutive events and an additional eclipse six
weeks later. The study's main purpose is the long wavelength (and thus limb
darkening-independent) characterization of GU Boo's light curve, allowing for
independent verification of the results of previous optical studies. Our
results confirm previously obtained system parameters. We further compare GU
Boo's measured 24m flux density to the value predicted by spectral fitting
and find no evidence for circumstellar dust. In addition to GU Boo, we
characterize (and show examples of) light curves of other objects in the field
of view. Analysis of these light curves serves to characterize the photometric
stability and repeatability of {\it Spitzer's} MIPS 24\micron array over short
(days) and long (weeks) timescales at flux densities between approximately
300--2,000Jy. We find that the light curve root mean square about the
median level falls into the 1--4% range for flux densities higher than 1mJy.
Finally, we comment on the fluctuations of the 24\micron background on short
and long timescales.Comment: ApJ accepted. 10 pages, 12 figure
Outbursts of EX Hydrae Revisited
We present optical spectroscopy of EX Hya during its 1991 outburst. This
outburst is characterised by strong irradiation of the front face of the
secondary star by the white dwarf, an overflowing stream which is seen strongly
in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the
binary and spin phases. Strong irradiation of the accretion curtain and that of
the inner regions of the disc led to strong emission of HeII and to the
suppression of the Hg and Hb emission.
Disc overflow was observed in quiescence in earlier studies, where the
overflow stream material was modulated at high velocities close to 1000 km/s.
In outburst, the overflowing material is modulated at even higher velocities
(~1500 km/s). These are streaming velocities down the field lines close to the
white dwarf. Evidence for material collecting near the outer edge of the disc
and corotating with the accretion curtain was observed. In decline, this
material and the accretion curtain obscured almost all the emission near binary
phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse
minimum. This has provided additional evidence for an extended accretion
curtain, and for the corotation of material with the accretion curtain at the
outer edge of the disc. From these observations we suggest that a mechanism
similar to that of Spruit & Taam, where outbursts result due to the storage and
release of matter outside the magnetosphere, triggers the outbursts of EX Hya.
This is followed by the irradiation of the secondary star due to accretion
induced radiation.Comment: 12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low
resolution. Paper accepted by the Monthly Notices of the Royal Astronomical
Societ
Measurement of the Surface Gravity of Boo
Direct angular size measurements of the G0IV subgiant Boo from the
Palomar Testbed Interferometer are presented, with limb-darkened angular size
of mas, which indicate a linear
radius of . A bolometric flux estimate of erg cms is computed, which indicates
an effective temperature of K and luminosity of for this object. Similar data are established for a check
star, HD 121860. The Boo results are compared to, and confirm, similar
parameters established by the {\it MOST} asteroseismology satellite. In
conjunction with the mass estimate from the {\it MOST} investigation, a surface
gravity of [cm s] is established for
Boo.Comment: To appear in March 1, 2007 ApJ v657 n
SearchCal: a Virtual Observatory tool for searching calibrators in optical long baseline interferometry. I: The bright object case
In long baseline interferometry, the raw fringe contrast must be calibrated
to obtain the true visibility and then those observables that can be
interpreted in terms of astrophysical parameters. The selection of suitable
calibration stars is crucial for obtaining the ultimate precision of
interferometric instruments like the VLTI. We have developed software SearchCal
that builds an evolutive catalog of stars suitable as calibrators within any
given user-defined angular distance and magnitude around the scientific target.
We present the first version of SearchCal dedicated to the bright-object case
V<=10; K<=5). Star catalogs available at the CDS are consulted via web
requests. They provide all the useful information for selecting of calibrators.
Missing photometries are computed with an accuracy of 0.1 mag and the missing
angular diameters are calculated with a precision better than 10%. For each
star the squared visibility is computed by taking the wavelength and the
maximum baseline of the foreseen observation into account.} SearchCal is
integrated into ASPRO, the interferometric observing preparation software
developed by the JMMC, available at the address: http://mariotti.fr
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