148 research outputs found
The UV, Optical, and IR Properties of SDSS Sources Detected by GALEX
We discuss the UV, optical, and IR properties of the SDSS sources detected by
GALEX as part of its All-sky Imaging Survey Early Release Observations.
Virtually all of the GALEX sources in the overlap region are detected by SDSS.
GALEX sources represent ~2.5% of all SDSS sources within these fields and about
half are optically unresolved. Most unresolved GALEX/SDSS sources are bright
blue turn-off thick disk stars and are typically detected only in the GALEX
near-UV band. The remaining unresolved sources include low-redshift quasars,
white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically
unresolved sources detected in both GALEX bands.
Almost all the resolved SDSS sources detected by GALEX are fainter than the
SDSS 'main' spectroscopic limit. These sources have colors consistent with
those of blue (spiral) galaxies (u-r<2.2), and most are detected in both GALEX
bands. Measurements of their UV colors allow much more accurate and robust
estimates of star-formation history than are possible using only SDSS data.
Indeed, galaxies with the most recent (<20 Myr) star formation can be robustly
selected from the GALEX data by requiring that they be brighter in the far-UV
than in the near-UV band. However, older starburst galaxies have UV colors
similar to AGN, and thus cannot be selected unambiguously on the basis of GALEX
fluxes alone.
With the aid of 2MASS data, we construct and discuss median 10 band
UV-optical-IR spectral energy distributions for turn-off stars, hot white
dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out
the high degree of correlation between the UV color and the contribution of the
UV flux to the UV-optical-IR flux of galaxies detected by GALEX.Comment: 35 pages, 11 figures, 3 tables; to appear in the AJ. PS with better
figures available from http://www.astro.washington.edu/agueros/pub
Improved age constraints for the AB Dor quadruple system - The binary nature of AB Dor B
We present resolved NACO photometry of the close binary AB Dor B in H- and
Ks-band. AB Dor B is itself known to be a wide binary companion to AB Dor A,
which in turn has a very low-mass close companion named AB Dor C. These four
known components make up the young and dynamically interesting system AB Dor,
which will likely become a benchmark system for calibrating theoretical
pre-main sequence evolutionary mass tracks for low-mass stars. However, for
this purpose the actual age has to be known, and this subject has been a matter
of discussion in the recent scientific literature. We compare our resolved
photometry of AB Dor Ba and Bb with theoretical and empirical isochrones in
order to constrain the age of the system. This leads to an age estimate of
about 50 to 100 Myr. We discuss the implications of such an age range for the
case of AB Dor C, and compare with other results in the literature.Comment: 7 pages, 6 figures, accepted for publication in A&
Cataclysmic Variables from SDSS 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.Comment: Accepted for publication in The Astronomical Journal, Vol. 126, Sep.
2003, 44 pages, 25 figures (now with adjacent captions), AASTeX v5.
The Whole is Greater than the Sum of the Parts: Optimizing the Joint Science Return from LSST, Euclid and WFIRST
The focus of this report is on the opportunities enabled by the combination
of LSST, Euclid and WFIRST, the optical surveys that will be an essential part
of the next decade's astronomy. The sum of these surveys has the potential to
be significantly greater than the contributions of the individual parts. As is
detailed in this report, the combination of these surveys should give us
multi-wavelength high-resolution images of galaxies and broadband data covering
much of the stellar energy spectrum. These stellar and galactic data have the
potential of yielding new insights into topics ranging from the formation
history of the Milky Way to the mass of the neutrino. However, enabling the
astronomy community to fully exploit this multi-instrument data set is a
challenging technical task: for much of the science, we will need to combine
the photometry across multiple wavelengths with varying spectral and spatial
resolution. We identify some of the key science enabled by the combined surveys
and the key technical challenges in achieving the synergies.Comment: Whitepaper developed at June 2014 U. Penn Workshop; 28 pages, 3
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The Ultraviolet, Optical, and Infrared Properties of Sloan Digital Sky Survey Sources Detected by GALEX
We discuss the ultraviolet, optical, and infrared properties of the Sloan Digital Sky Survey (SDSS) sources detected by the Galaxy Evolution Explorer (GALEX) as part of its All-sky Imaging Survey Early Release Observations. Virtually all (>99%) the GALEX sources in the overlap region are detected by SDSS; those without an SDSS counterpart within our 6'' search radius are mostly unflagged GALEX artifacts. GALEX sources represent ~2.5% of all SDSS sources within these fields, and about half are optically unresolved. Most unresolved GALEX-SDSS sources are bright (r < 18 mag), blue, turnoff, thick-disk stars and are typically detected only in the GALEX near-ultraviolet (NUV) band. The remaining unresolved sources include low-redshift quasars (z < 2.2), white dwarfs, and white dwarf–M dwarf pairs, and these dominate the optically unresolved sources detected in both GALEX bands. Almost all the resolved SDSS sources detected by GALEX are fainter than the SDSS main spectroscopic limit. (Conversely, of the SDSS galaxies in the main spectroscopic sample, about 40% are detected in at least one GALEX band.) These sources have colors consistent with those of blue (spiral) galaxies (u - r < 2.2), and most are detected in both GALEX bands. Measurements of their UV colors allow much more accurate and robust estimates of star formation history than are possible using only SDSS data. Indeed, galaxies with the most recent (lesssim20 Myr) star formation can be robustly selected from the GALEX data by requiring that they be brighter in the far-ultraviolet (FUV) than in the NUV band. However, older starburst galaxies have UV colors similar to those of active galactic nuclei and thus cannot be selected unambiguously on the basis of GALEX fluxes alone. Additional information, such as spatially resolved FUV emission, optical morphology, or X-ray and radio data, is needed before blue GALEX colors can be unambiguously interpreted as a sign of recent star formation. With the aid of Two Micron All Sky Survey data, we construct and discuss median 10-band UV through infrared spectral energy distributions for turnoff stars, hot white dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out the high degree of correlation between the UV color and the contribution of the UV flux to the UV through infrared flux of galaxies detected by GALEX; for example, this correlation can be used to predict the SDSS z-band measurement, using only two GALEX fluxes, with a scatter of only 0.7 mag
The MUSCLES Treasury Survey. II. Intrinsic Lyα and extreme ultraviolet spectra of K and M dwarfs with exoplanets
This work was supported by NASA grants HST-GO-12464.01 and HST-GO-13650.01 to the University of Colorado at Boulder. Sarah Rugheimer would like to acknowledge support from the Simons Foundation (339489, Rugheimer).The ultraviolet (UV) spectral energy distributions (SEDs) of low-mass (K- and M-type) stars play a critical role in the heating and chemistry of exoplanet atmospheres, but are not observationally well-constrained. Direct observations of the intrinsic flux of the Lyα line (the dominant source of UV photons from low-mass stars) are challenging, as interstellar H i absorbs the entire line core for even the closest stars. To address the existing gap in empirical constraints on the UV flux of K and M dwarfs, the MUSCLES Hubble Space Telescope Treasury Survey has obtained UV observations of 11 nearby M and K dwarfs hosting exoplanets. This paper presents the Lyα and extreme-UV spectral reconstructions for the MUSCLES targets. Most targets are optically inactive, but all exhibit significant UV activity. We use a Markov Chain Monte Carlo technique to correct the observed Lyα profiles for interstellar absorption, and we employ empirical relations to compute the extreme-UV SED from the intrinsic Lyα flux in ∼100 bins from 100-1170. The reconstructed Lyα profiles have 300 km s-1 broad cores, while >1% of the total intrinsic Lyα flux is measured in extended wings between 300 and 1200 km s-1. The Lyα surface flux positively correlates with the Mg ii surface flux and negatively correlates with the stellar rotation period. Stars with larger Lyα surface flux also tend to have larger surface flux in ions formed at higher temperatures, but these correlations remain statistically insignificant in our sample of 11 stars. We also present H i column density measurements for 10 new sightlines through the local interstellar medium.Publisher PDFPeer reviewe
Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
We present the discovery of the Kepler-20 planetary system, which we
initially identified through the detection of five distinct periodic transit
signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We
find a stellar effective temperature Teff=5455+-100K, a metallicity of
[Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an
estimate of the stellar density from the transit light curves we deduce a
stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of
Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our
results strongly disfavor the possibility that these result from astrophysical
false positives. We conclude that the planetary scenario is more likely than
that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5
(Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as
planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is
independently disfavored by the achromaticity of the transit: From Spitzer data
gathered at 4.5um, we infer a ratio of the planetary to stellar radii of
0.075+-0.015 (Kepler-20c) and 0.065+-0.011 (Kepler-20d), consistent with each
of the depths measured in the Kepler optical bandpass. We determine the orbital
periods and physical radii of the three confirmed planets to be 3.70d and
1.91^{+0.12}_{-0.21} Rearth for Kepler-20b, 10.85 d and 3.07^{+0.20}_{-0.31}
Rearth for Kepelr-20c, and 77.61 d and 2.75^{+0.17}_{-0.30} Rearth for
Kepler-20d. From multi-epoch radial velocities, we determine the masses of
Kepler-20b and Kepler-20c to be 8.7\+-2.2 Mearth and 16.1+-3.5 Mearth,
respectively, and we place an upper limit on the mass of Kepler-20d of 20.1
Mearth (2 sigma).Comment: accepted by ApJ, 58 pages, 12 figures revised Jan 2012 to correct
table 2 and clarify planet parameter extractio
Estimating the frequency of extremely energetic solar events, based on solar, stellar, lunar, and terrestrial records
The most powerful explosions on the Sun [...] drive the most severe
space-weather storms. Proxy records of flare energies based on SEPs in
principle may offer the longest time base to study infrequent large events. We
conclude that one suggested proxy, nitrate concentrations in polar ice cores,
does not map reliably to SEP events. Concentrations of select radionuclides
measured in natural archives may prove useful in extending the time interval of
direct observations up to ten millennia, but as their calibration to solar
flare fluences depends on multiple poorly known properties and processes, these
proxies cannot presently be used to help determine the flare energy frequency
distribution. Being thus limited to the use of direct flare observations, we
evaluate the probabilities of large-energy solar explosions by combining solar
flare observations with an ensemble of stellar flare observations. We conclude
that solar flare energies form a relatively smooth distribution from small
events to large flares, while flares on magnetically-active, young Sun-like
stars have energies and frequencies markedly in excess of strong solar flares,
even after an empirical scaling with the mean activity level of these stars. In
order to empirically quantify the frequency of uncommonly large solar flares
extensive surveys of stars of near-solar age need to be obtained, such as is
feasible with the Kepler satellite. Because the likelihood of flares larger
than approximately X30 remains empirically unconstrained, we present indirect
arguments, based on records of sunspots and on statistical arguments, that
solar flares in the past four centuries have likely not substantially exceeded
the level of the largest flares observed in the space era, and that there is at
most about a 10% chance of a flare larger than about X30 in the next 30 years.Comment: 14 pages, 3 figures (in press as of 2012/06/18); Journal of
Geophysical Research (Space Physics), 201
Photometric transit search for planets around cool stars from the western Italian Alps: A pilot study
[ABRIDGED] In this study, we set out to a) demonstrate the sensitivity to <4
R_E transiting planets with periods of a few days around our program stars, and
b) improve our knowledge of some astrophysical properties(e.g., activity,
rotation) of our targets by combining spectroscopic information and our
differential photometric measurements. We achieve a typical nightly RMS
photometric precision of ~5 mmag, with little or no dependence on the
instrumentation used or on the details of the adopted methods for differential
photometry. The presence of correlated (red) noise in our data degrades the
precision by a factor ~1.3 with respect to a pure white noise regime. Based on
a detailed stellar variability analysis, a) we detected no transit-like events;
b) we determined photometric rotation periods of ~0.47 days and ~0.22 days for
LHS 3445 and GJ 1167A, respectively; c) these values agree with the large
projected rotational velocities (~25 km/s and ~33 km/s, respectively) inferred
for both stars based on the analysis of archival spectra; d) the estimated
inclinations of the stellar rotation axes for LHS 3445 and GJ 1167A are
consistent with those derived using a simple spot model; e) short-term,
low-amplitude flaring events were recorded for LHS 3445 and LHS 2686. Finally,
based on simulations of transit signals of given period and amplitude injected
in the actual (nightly reduced) photometric data for our sample, we derive a
relationship between transit detection probability and phase coverage. We find
that, using the BLS search algorithm, even when phase coverage approaches 100%,
there is a limit to the detection probability of ~90%. Around program stars
with phase coverage >50% we would have had >80% chances of detecting planets
with P0.5%, corresponding to minimum
detectable radii in the range 1.0-2.2 R_E. [ABRIDGED]Comment: 23 pages, 17 figures, 7 tables. Accepted for publication in MNRA
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