1,982 research outputs found
Trigonometric Parallaxes for 1,507 Nearby Mid-to-Late M-dwarfs
The MEarth survey is a search for small rocky planets around the smallest,
nearest stars to the Sun as identified by high proper motion with red colors.
We augmented our planetary search time series with lower cadence astrometric
imaging and obtained two million images of approximately 1800 stars suspected
to be mid-to-late M dwarfs. We fit an astrometric model to MEarth's images for
1507 stars and obtained trigonometric distance measurements to each star with
an average precision of 5 milliarcseconds. Our measurements, combined with the
2MASS photometry, allowed us to obtain an absolute K_s magnitude for each star.
In turn, this allows us to better estimate the stellar parameters than those
obtained with photometric estimates alone and to better prioritize the targets
chosen to monitor at high cadence for planetary transits. The MEarth sample is
mostly complete out to a distance of 25 parsecs for stars of type M5.5V and
earlier, and mostly complete for later type stars out to 20 parsecs. We find
eight stars that are within ten parsecs of the Sun for which there did not
exist a published trigonometric parallax distance estimate. We release with
this work a catalog of the trigonometric parallax measurements for 1,507
mid-to-late M-dwarfs, as well as new estimates of their masses and radii.Comment: ApJ, accepted. 36 pages, 8 figures, 2 tables. Please find our data
table here: http://www.cfa.harvard.edu/MEarth/DataDR2.htm
On the Apparent Orbital Inclination Change of the Extrasolar Transiting Planet TrES-2b
On June 15, 2009 UT the transit of TrES-2b was detected using the University
of Arizona's 1.55 meter Kuiper Telescope with 2.0-2.5 millimag RMS accuracy in
the I-band. We find a central transit time of
HJD, an orbital period of days, and an
inclination angle of , which is consistent with our
re-fit of the original I-band light curve of O'Donovan et al. (2006) where we
find . We calculate an insignificant inclination
change of over the last 3 years, and as
such, our observations rule out, at the level, the apparent
change of orbital inclination to as
predicted by Mislis and Schmitt (2009) and Mislis et al. (2010) for our epoch.
Moreover, our analysis of a recently published Kepler Space Telescope light
curve (Gilliland et al. 2010) for TrES-2b finds an inclination of for a similar epoch. These Kepler results definitively
rule out change in as a function of time. Indeed, we detect no significant
changes in any of the orbital parameters of TrES-2b.Comment: 19 pages, 1 table, 7 figures. Re-submitted to ApJ, January 14, 201
A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100 Hour Spitzer Campaign
We present the results of a search for additional bodies in the GJ 1132
system through two methods: photometric transits and transit timing variations
of the known planet. We collected 21 transit observations of GJ 1132b with the
MEarth-South array since 2015. We obtained 100 near-continuous hours of
observations with the Space Telescope, including two transits of GJ
1132b and spanning 60\% of the orbital phase of the maximum period at which
bodies coplanar with GJ 1132b would pass in front of the star. We exclude
transits of additional Mars-sized bodies, such as a second planet or a moon,
with a confidence of 99.7\%. When we combine the mass estimate of the star
(obtained from its parallax and apparent band magnitude) with the stellar
density inferred from our high-cadence light curve (assuming zero
eccentricity), we measure the stellar radius of GJ 1132 to be
, and we refine the radius measurement of
GJ 1132b to . Combined with HARPS RV measurements, we
determine the density of GJ 1132b to be \ g cm, with the
mass determination dominating this uncertainty. We refine the ephemeris of the
system and find no evidence for transit timing variations, which would be
expected if there was a second planet near an orbital resonance with GJ 1132b.Comment: 29 pages, 4 Tables, 8 Figures, Submitted to ApJ. Comments welcom
A Revised Orbital Ephemeris for HAT-P-9b
We present here three transit observations of HAT-P-9b taken on 14 February
2010, 18 February 2010, and 05 April 2010 UT from the University of Arizona's
1.55 meter Kuiper telescope on Mt. Bigelow. Our transit light curves were
obtained in the I filter for all our observations, and underwent the same
reduction process. All three of our transits deviated significantly
(approximately 24 minutes earlier) from the ephemeris of Shporer et al. (2008).
However, due to the large time span between our observed transits and those of
Shporer et al. (2008), a 6.5 second (2 sigma) shift downwards in orbital period
from the value of Shporer et al. (2008) is sufficient to explain all available
transit data. We find a new period of 3.922814 +/- 0.000002 days for HAT-P-9b
with no evidence for significant nonlinearities in the transit period.Comment: 10 pages, 3 figure
The rotation and Galactic kinematics of mid M dwarfs in the Solar Neighborhood
Rotation is a directly-observable stellar property, and drives magnetic field
generation and activity through a magnetic dynamo. Main sequence stars with
masses below approximately 0.35Msun (mid-to-late M dwarfs) are
fully-convective, and are expected to have a different type of dynamo mechanism
than solar-type stars. Measurements of their rotation rates provide insights
into these mechanisms, but few rotation periods are available for these stars
at field ages. Using photometry from the MEarth transit survey, we measure
rotation periods for 387 nearby, mid-to-late M dwarfs in the Northern
hemisphere, finding periods from 0.1 to 140 days. The typical detected rotator
has stable, sinusoidal photometric modulations at a semi-amplitude of 0.5 to
1%. We find no period-amplitude relation for stars below 0.25Msun and an
anti-correlation between period and amplitude for higher-mass M dwarfs. We
highlight the existence of older, slowly-rotating stars without H{\alpha}
emission that nevertheless have strong photometric variability. The Galactic
kinematics of our sample is consistent with the local population of G and K
dwarfs, and rotators have metallicities characteristic of the Solar
Neighborhood. We use the W space velocities and established age-velocity
relations to estimate that stars with P<10 days are on average <2 Gyrs, and
that those with P>70 days are about 5 Gyrs. The period distribution is mass
dependent: as the mass decreases, the slowest rotators at a given mass have
longer periods, and the fastest rotators have shorter periods. We find a lack
of stars with intermediate rotation periods. [Abridged]Comment: Accepted to ApJ. Machine readable tables and additional figures are
available in the published article or on reques
A Tentative Detection of a Starspot During Consecutive Transits of an Extrasolar Planet from the Ground: No Evidence of a Double Transiting Planet System Around TrES-1
There have been numerous reports of anomalies during transits of the planet
TrES-1b. Recently, Rabus and coworkers' analysis of HST observations lead them
to claim brightening anomalies during transit might be caused by either a
second transiting planet or a cool starspot. Observations of two consecutive
transits are presented here from the University of Arizona's 61-inch Kuiper
Telescope on May 12 and May 15, 2008 UT. A 5.4 +/- 1.7 mmag (0.54 +/- 0.17%)
brightening anomaly was detected during the first half of the transit on May 12
and again in the second half of the transit on May 15th. We conclude that this
is a tentative detection of a r greater than or equal to 6 earth radii starspot
rotating on the surface of the star. We suggest that all evidence to date
suggest TrES-1 has a spotty surface and there is no need to introduce a second
transiting planet in this system to explain these anomalies. We are only able
to constrain the rotational period of the star to 40.2 +22.9 -14.6 days, due to
previous errors in measuring the alignment of the stellar spin axis with the
planetary orbital axis. This is consistent with the previously observed P_obs =
33.2 +22.3 -14.3 day period. We note that this technique could be applied to
other transiting systems for which starspots exist on the star in the transit
path of the planet in order to constrain the rotation rate of the star.
(abridged)Comment: 21 pages, 3 tables, 6 figures, Accepted to Ap
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