164 research outputs found
VARTOOLS: A Program for Analyzing Astronomical Time-Series Data
This paper describes the VARTOOLS program, which is an open-source
command-line utility, written in C, for analyzing astronomical time-series
data, especially light curves. The program provides a general-purpose set of
tools for processing light curves including signal identification, filtering,
light curve manipulation, time conversions, and modeling and simulating light
curves. Some of the routines implemented include the Generalized Lomb-Scargle
periodogram, the Box-Least Squares transit search routine, the Analysis of
Variance periodogram, the Discrete Fourier Transform including the CLEAN
algorithm, the Weighted Wavelet Z-Transform, light curve arithmetic, linear and
non-linear optimization of analytic functions including support for Markov
Chain Monte Carlo analyses with non-trivial covariances, characterizing and/or
simulating time-correlated noise, and the TFA and SYSREM filtering algorithms,
among others. A mechanism is also provided for incorporating a user's own
compiled processing routines into the program. VARTOOLS is designed especially
for batch processing of light curves, including built-in support for parallel
processing, making it useful for large time-domain surveys such as searches for
transiting planets. Several examples are provided to illustrate the use of the
program.Comment: 83 pages, 5 figures, accepted for publication in Astronomy and
Computing, code available at
http://www.astro.princeton.edu/~jhartman/vartools.htm
On the Rotation Period of (90377) Sedna
We present precise, ~1%, r-band relative photometry of the unusual solar
system object (90377) Sedna. Our data consist of 143 data points taken over
eight nights in October 2004 and January 2005. The RMS variability over the
longest contiguous stretch of five nights of data spanning nine days is only
1.3%. This subset of data alone constrain the amplitude of any long-period
variations with period P to be A<1% (P/20 days)^2. Over the course of any given
5-hour segment, the data exhibits significant linear trends not seen in a
comparison star of similar magnitude, and in a few cases these segments show
clear evidence for curvature at the level of a few millimagnitudes per hour^2.
These properties imply that the rotation period of Sedna is O(10 hours), cannot
be 10 days, unless the intrinsic light curve has
significant and comparable power on multiple timescales, which is unlikely. A
sinusoidal fit yields a period of P=(10.273 +/- 0.002) hours and semi-amplitude
of A=(1.1 +/- 0.1)%. There are additional acceptable fits with flanking periods
separated by ~3 minutes, as well as another class of fits with P ~ 18 hours,
although these later fits appear less viable based on visual inspection. Our
results indicate that the period of Sedna is likely consistent with typical
rotation periods of solar system objects, thus obviating the need for a massive
companion to slow its rotation.Comment: 7 pages, 4 figures, 2.5 tables. Final ApJL version, minor changes.
Full light curve data in tex
On the hierarchical triple nature of the former red nova precursor candidate KIC 9832227
We revisit the issue of period variation of the recently claimed red nova
precursor candidate KIC 9832227. By using the data gathered during the main
mission of the Kepler satellite, those collected by ground-based wide-field
surveys and other monitoring programs (such as ASAS-SN), we find that the
currently available timing data strongly support a model consisting of the
known W UMa binary and a distant low-mass companion with an orbital period of
~13.5 years. The period of the W UMa component exhibits a linear period
decrease with a pace of (1.10+/-0.05)x10^{-6} days per year, within the range
of many other similar systems. This rate of decrease is several orders of
magnitude lower than that of V1309 Sco, the first (and so far the only)
well-established binary precursor of a nova observed a few years before the
outburst. The high-fidelity fit of the timing data and the conformity of the
derived minimum mass of (0.38+/-0.02) Msun of the outer companion from these
data with the limit posed by the spectroscopic non-detection of this component,
are in agreement with the suggested hierarchical nature of this system.Comment: Submitted to A&A; 11 pages, ~0.6 Mb, after the first favorable
referee repor
A Search for Variable Stars in the Globular Cluster M4 with K2
We extract light curves for 4554 objects with in the K2 superstamp
observations of the globular cluster M4, including 3784 cluster members, and
search for variability. Among cluster member objects, we detect 66 variables,
of which 52 are new discoveries. Among objects not belonging to the cluster, we
detect 24 variables, of which 20 are new discoveries. We additionally discover
57 cluster-member suspected variables, 10 cluster-non-member suspected
variables, and four variables with ambiguous cluster membership. Our light
curves reach sub-millimagnitude precision for the cluster horizontal branch,
permitting us to detect asteroseismic activity in six horizontal branch stars
outside the instability strip and one inside the strip but with only ~1 mmag
amplitude variability. 19 additional stars along the red giant branch also have
detected asteroseismic variability. Several eclipsing binaries are found in the
cluster, including a 4.6-day detached eclipsing binary and an EW-class
eclipsing binary, as well as an EW with uncertain cluster membership and three
other candidate EWs. A 22-day detached eclipsing binary is also found outside
the cluster. We identify a candidate X-ray binary that is a cluster member with
quiescent and periodic ~20 mmag optical variability. We also obtain
high-precision light curves for ten of the previously known RR Lyrae variables
in the cluster and identify one as a candidate Blazhko variable with a Blazhko
period in excess of 78 days. We make our light curves publicly available.Comment: 48 pages, 21 figures, 5 tables; online material: Table 1 and light
curve data; accepted for publication in ApJ
K2-113b: A dense hot-Jupiter transiting a solar analogue
We present the discovery of K2-113b, a dense hot-Jupiter discovered using
photometry from Campaign 8 of the Kepler-2 (K2) mission and high-resolution
spectroscopic follow up obtained with the FEROS spectrograph. The planet orbits
a solar analogue in a day orbit,
has a radius of and a mass of
. With a density of gr/cm,
the planet is among the densest systems known having masses below 2 and
, and is just above the temperature limit at which inflation
mechanisms are believed to start being important. Based on its mass and radius,
we estimate that K2-113b should have a heavy element content on the order of
110 or greater.Comment: 8 pages, 7 figures. Accepted to MNRAS; added new photometry from
newest version of EVEREST, which allows for a constrain on the secondary
eclipse dept
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