2,119 research outputs found
The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to
~1000 stars at 5 Hz simultaneously with four small telescopes to detect
occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey
presents a number of challenges, in particular the fact that the occultation
events we are searching for are extremely rare and are typically manifested as
slight flux drops for only one or two consecutive time series measurements. We
have developed a statistical analysis technique to search the multi-telescope
data set for simultaneous flux drops which provides a robust false positive
rejection and calculation of event significance. In this paper, we describe in
detail this statistical technique and its application to the TAOS data set.Comment: 15 pages, 14 figures. Submitted to PAS
Large-Amplitude Ultraviolet Variations in the RR Lyrae Star ROTSE-I J143753.84+345924.8
The NASA Galaxy Evolution Explorer (GALEX) satellite has obtained
simultaneous near and far ultraviolet light curves of the ROTSE-I Catalog RR
Lyrae ab-type variable star J143753.84+345924.8. A series of 38 GALEX Deep
Imaging Survey observations well distributed in phase within the star's
0.56432d period shows an AB=4.9mag variation in the far UV (1350-1750A) band
and an AB=1.8mag variation in the near UV (1750-2750A) band, compared with only
a 0.8mag variation in the broad, unfiltered ROTSE-I (4500-10000A) band. These
GALEX UV observations are the first to reveal a large RR Lyrae amplitude
variation at wavelengths below 1800A. We compare the GALEX and ROTSE-I
observations to predictions made by recent Kurucz stellar atmosphere models. We
use published physical parameters for the comparable period (0.57433d),
well-observed RR Lyrae star WY Antliae to compute predicted FUV, NUV, and
ROTSE-I light curves for J143753.84+345924.8. The observed light curves agree
with the Kurucz predictions for [Fe/H]=-1.25 to within AB=0.2mag in the GALEX
NUV and ROTSE-I bands, and within 0.5mag in the FUV. At all metallicities
between solar and one hundredth solar, the Kurucz models predict 6-8mag of
variation at wavelengths between 1000-1700A. Other variable stars with similar
temperature variations, such as Cepheids, should also have large-amplitude FUV
light curves, observable during the ongoing GALEX imaging surveys.Comment: This paper will be published as part of the Galaxy Evolution Explorer
(GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of
papers will be available at http:/www.galex.caltech.edu/PUBLICATIONS after
November 22, 200
The GALEX UV luminosity function of the cluster of galaxies Abell 1367
We present the GALEX NUV (2310 A) and FUV (1530 A) galaxy luminosity
functions of the nearby cluster of galaxies A1367 in the magnitude range -20.3<
M_AB < -13.3. The luminosity functions are consistent with previous (~ 2 mag
shallower) estimates based on the FOCA and FAUST experiments, but display a
steeper faint-end slope than the GALEX luminosity function for local field
galaxies. Using spectro-photometric optical data we select out star-forming
systems from quiescent galaxies and study their separate contributions to the
cluster luminosity function. We find that the UV luminosity function of cluster
star-forming galaxies is consistent with the field. The difference between the
cluster and field LF is entirely due to the contribution at low luminosities
(M_AB >-16 mag) of non star-forming, early-type galaxies that are significantly
over dense in clusters.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in
Astrophysical Journal Letter
The Taiwanese-American Occultation Survey Project Stellar Variability. II. Detection of 15 Variable Stars
The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data—covering timescales from a fraction of a second to a few hundred days—are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (R.A. = 17^(h)30^(m)6^(s).7, decl. = 27°17'30", J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 deg^2 field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the light curves, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, δ Scuti, SX Phonencis, semi-regular, and eclipsing binaries
GALEX UV Spectroscopy and Deep Imaging of LIRGs in the ELAIS S1 field
The ELAIS S1 field was observed by GALEX in both its Wide Spectroscopic and
Deep Imaging Survey modes. This field was previously observed by the Infrared
Space Observatory and we made use of the catalogue of multi-wavelength data
published by the ELAIS consortium to select galaxies common to the two samples.
Among the 959 objects with GALEX spectroscopy, 88 are present in the ELAIS
catalog and 19 are galaxies with an optical spectroscopic redshift. The
distribution of redshifts covers the range . The selected galaxies
have bolometric IR luminosities (deduced from the flux using ISOCAM) which means that we cover a wide range of galaxies from
normal to Ultra Luminous IR Galaxies. The mean () UV luminosity (not
corrected for extinction) amounts to
L_\sun for the low-z () sample. The UV slope (assuming
) correlates with the GALEX FUV-NUV color if
the sample is restricted to galaxies below . Taking advantage of the
UV and IR data, we estimate the dust attenuation from the IR/UV ratio and
compare it to the UV slope . We find that it is not possible to uniquely
estimate the dust attenuation from for our sample of galaxies. These
galaxies are highly extinguished with a median value .
Once the dust correction applied, the UV- and IR-based SFRs correlate. For the
closest galaxy with the best quality spectrum, we see a feature consistent with
being produced by a bump near 220nm in the attenuation curve.Comment: This paper has been published as part of the GALEX ApJL Special Issue
(ApJ 619, L63
The Taiwanese-American Occultation Survey: The Multi-Telescope Robotic Observatory
The Taiwanese-American Occultation Survey (TAOS) operates four fully
automatic telescopes to search for occultations of stars by Kuiper Belt
Objects. It is a versatile facility that is also useful for the study of
initial optical GRB afterglows. This paper provides a detailed description of
the TAOS multi-telescope system, control software, and high-speed imaging.Comment: 11 pages, 11 figure
The TAOS Project Stellar Variability I. Detection of Low-Amplitude delta Scuti Stars
We analyzed data accumulated during 2005 and 2006 by the Taiwan-American
Occultation Survey (TAOS) in order to detect short-period variable stars
(periods of <~ 1 hour) such as delta Scuti. TAOS is designed for the detection
of stellar occultation by small-size Kuiper Belt Objects (KBOs) and is
operating four 50cm telescopes at an effective cadence of 5Hz. The four
telescopes simultaneously monitor the same patch of the sky in order to reduce
false positives. To detect short-period variables, we used the Fast Fourier
Transform algorithm (FFT) inasmuch as the data points in TAOS light-curves are
evenly spaced. Using FFT, we found 41 short-period variables with amplitudes
smaller than a few hundredths of a magnitude and periods of about an hour,
which suggest that they are low-amplitude delta Scuti stars (LADS). The
light-curves of TAOS delta Scuti stars are accessible online at the Time Series
Center website (http://timemachine.iic.harvard.edu)Comment: Accepted for publication in A
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