594 research outputs found
Secretly Eccentric: The Giant Planet and Activity Cycle of GJ 328
We announce the discovery of a ~2 Jupiter-mass planet in an eccentric 11-year
orbit around the K7/M0 dwarf GJ 328. Our result is based on 10 years' worth of
radial velocity (RV) data from the Hobby-Eberly and Harlan J. Smith telescopes
at McDonald Observatory, and from the Keck Telescope at Mauna Kea. Our analysis
of GJ 328's magnetic activity via the Na I D features reveals a long-period
stellar activity cycle, which creates an additional signal in the star's RV
curve with amplitude 6-10 m/s. After correcting for this stellar RV
contribution, we see that the orbit of the planet is more eccentric than
suggested by the raw RV data. GJ 328b is currently the most massive,
longest-period planet discovered around a low-mass dwarf.Comment: Accepted for publication in Ap
Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum
We present the first ground-based detection of sodium absorption in the
transmission spectrum of an extrasolar planet. Absorption due to the atmosphere
of the extrasolar planet HD189733b is detected in both lines of the NaI
doublet. High spectral resolution observations were taken of eleven transits
with the High Resolution Spectrograph (HRS) on the 9.2 meter Hobby-Eberly
Telescope (HET). The NaI absorption in the transmission spectrum due to
HD189733b is (-67.2 +/- 20.7) x 10^-5 deeper in the ``narrow'' spectral band
that encompasses both lines relative to adjacent bands. The 1-sigma error
includes both random and systematic errors, and the detection is >3-sigma. This
amount of relative absorption in NaI for HD189733b is ~3x larger than detected
for HD209458b by Charbonneau et al. (2002), and indicates these two
hot-Jupiters may have significantly different atmospheric properties.Comment: 12 pages, 2 figures; Accepted for publication in ApJ Letter
Stellar Activity and its Implications for Exoplanet Detection on GJ 176
We present an in-depth analysis of stellar activity and its effects on radial
velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10 years from
the High Resolution Spectrograph on the Hobby-Eberly Telescope. These data are
supplemented with spectra from previous observations with the HIRES and HARPS
spectrographs, and V- and R-band photometry taken over 6 years at the Dyer and
Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth
exoplanet in an 8.8-day orbit. However, the velocities of this star are also
known to be contaminated by activity, particularly at the 39-day stellar
rotation period. We have examined the magnetic activity of GJ 176 using the
sodium I D lines, which have been shown to be a sensitive activity tracer in
cool stars. In addition to rotational modulation, we see evidence of a
long-term trend in our Na I D index, which may be part of a long-period
activity cycle. The sodium index is well correlated with our RVs, and we show
that this activity trend drives a corresponding slope in RV. Interestingly, the
rotation signal remains in phase in photometry, but not in the spectral
activity indicators. We interpret this phenomenon as the result of one or more
large spot complexes or active regions which dominate the photometric
variability, while the spectral indices are driven by the overall magnetic
activity across the stellar surface. In light of these results, we discuss the
potential for correcting activity signals in the RVs of M dwarfs.Comment: Accepted for publication in Ap
Evidence for Past Subduction Earthquakes at a Plate Boundary with Widespread Upper Plate Faulting: Southern Hikurangi Margin, New Zealand
At the southern Hikurangi margin, New Zealand, we use salt marsh stratigraphy, sedimentology, micropaleontology, and radiocarbon dating to document evidence of two earthquakes producing coseismic subsidence and (in one case) a tsunami over the past 1000 yrs. The earthquake at 520-470 yrs before present (B.P.) produced 0.25 +/- 0.1 m of subsidence at Big Lagoon. The earthquake at 880-800 yrs B.P. produced 0.45 +/- 0.1 m of subsidence at Big Lagoon and was accompanied by a tsunami that inundated >= 360 m inland with a probable height of >= 3.3 m. Distinguishing the effects of upper plate faulting from plate interface earthquakes is a significant challenge at this margin. We use correlation with regional upper plate paleoearthquake chronologies and elastic dislocation modeling to determine that the most likely cause of the subsidence and tsunami events is subduction interface rupture, although the older event may have been a synchronous subduction interface and upper plate fault rupture. The southern Hikurangi margin has had no significant (M > 6.5) documented subduction interface earthquakes in historic times, and previous assumptions that this margin segment is prone to rupture in large to great earthquakes were based on seismic and geodetic evidence of strong contemporary plate coupling. This is the first geologic evidence to confirm that the southern Hikurangi margin ruptures in large earthquakes. The relatively short-time interval between the two subduction earthquakes (similar to 350 yrs) is shorter than in current seismic-hazard models.GNSEQC Biennial ProjectNew Zealand Natural Hazards Research Platform and Foundation for Research Science and TechnologyInstitute for Geophysic
The McDonald Observatory Planet Search: New Long-Period Giant Planets, and Two Interacting Jupiters in the HD 155358 System
We present high-precision radial velocity (RV) observations of four
solar-type (F7-G5) stars - HD 79498, HD 155358, HD 197037, and HD 220773 -
taken as part of the McDonald Observatory Planet Search Program. For each of
these stars, we see evidence of Keplerian motion caused by the presence of one
or more gas giant planets in long-period orbits. We derive orbital parameters
for each system, and note the properties (composition, activity, etc.) of the
host stars. While we have previously announced the two-gas-giant HD 155358
system, we now report a shorter period for planet c. This new period is
consistent with the planets being trapped in mutual 2:1 mean-motion resonance.
We therefore perform an in-depth stability analysis, placing additional
constraints on the orbital parameters of the planets. These results demonstrate
the excellent long-term RV stability of the spectrometers on both the Harlan J.
Smith 2.7 m telescope and the Hobby-Eberly telescope.Comment: 38 pages, 10 figures, 6 tables. Accepted for publication in Ap
Revisiting rho 1 Cancri e: A New Mass Determination Of The Transiting super-Earth
We present a mass determination for the transiting super-Earth rho 1 Cancri e
based on nearly 700 precise radial velocity (RV) measurements. This extensive
RV data set consists of data collected by the McDonald Observatory planet
search and published data from Lick and Keck observatories (Fischer et al.
2008). We obtained 212 RV measurements with the Tull Coude Spectrograph at the
Harlan J. Smith 2.7 m Telescope and combined them with a new Doppler reduction
of the 131 spectra that we have taken in 2003-2004 with the
High-Resolution-Spectrograph (HRS) at the Hobby-Eberly Telescope (HET) for the
original discovery of rho 1 Cancri e. Using this large data set we obtain a
5-planet Keplerian orbital solution for the system and measure an RV
semi-amplitude of K = 6.29 +/- 0.21 m/s for rho 1 Cnc e and determine a mass of
8.37 +/- 0.38 M_Earth. The uncertainty in mass is thus less than 5%. This
planet was previously found to transit its parent star (Winn et al. 2011,
Demory et al. 2011), which allowed them to estimate its radius. Combined with
the latest radius estimate from Gillon et al. (2012), we obtain a mean density
of rho = 4.50 +/- 0.20 g/cm^3. The location of rho 1 Cnc e in the mass-radius
diagram suggests that the planet contains a significant amount of volitales,
possibly a water-rich envelope surrounding a rocky core.Comment: 16 pages, 5 figures, accepted for publication in the Astrophysical
Journal (the 300+ RV measurements will be published as online tables or can
be obtained from the author
A Second Giant Planet in 3:2 Mean-Motion Resonance in the HD 204313 System
We present 8 years of high-precision radial velocity (RV) data for HD 204313
from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is
known to have a giant planet (M sin i = 3.5 M_J) on a ~1900-day orbit, and a
Neptune-mass planet at 0.2 AU. Using our own data in combination with the
published CORALIE RVs of Segransan et al. (2010), we discover an outer Jovian
(M sin i = 1.6 M_J) planet with P ~ 2800 days. Our orbital fit suggests the
planets are in a 3:2 mean motion resonance, which would potentially affect
their stability. We perform a detailed stability analysis, and verify the
planets must be in resonance.Comment: Accepted for publication in Ap
Radial Velocity Observations and Light Curve Noise Modeling Confirm That Kepler-91b is a Giant Planet Orbiting a Giant Star
Kepler-91b is a rare example of a transiting hot Jupiter around a red giant
star, providing the possibility to study the formation and composition of hot
Jupiters under different conditions compared to main-sequence stars. However,
the planetary nature of Kepler-91b, which was confirmed using phase-curve
variations by Lillo-Box et al., was recently called into question based on a
re-analysis of Kepler data. We have obtained ground-based radial velocity
observations from the Hobby-Eberly Telescope and unambiguously confirm the
planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial
velocity data. The star exhibits temporally correlated noise due to stellar
granulation which we model as a Gaussian Process. We hypothesize that it is
this noise component that led previous studies to suspect Kepler-91b to be a
false positive. Our work confirms the conclusions presented by Lillo-Box et al.
that Kepler-91b is a 0.73+/-0.13 Mjup planet orbiting a red giant star.Comment: Published in Ap
Further evidence for the planet around 51 Pegasi
The discovery of the planet around the solar-type star 51 Pegasi marked a
watershed in the search for extrasolar planets. Since then seven other
solar-type stars have been discovered, of which several have surprisingly short
orbital periods, like the planet around 51 Peg. These planets were detected
using the indirect technique of measuring variations in the Doppler shifts of
lines in the spectra of the primary stars. But it is possible that oscillations
of the stars themselves (or other effects) could mimic the signature of the
planets, particularly around the short-period planets. The apparent lack of
spectral and brightness variations, however, led to widespread acceptance that
there is a planet around 51 Peg. This conclusion was challenged by the
observation of systematic variations in the line profile shapes of 51 Peg,
which suggested stellar oscillations. If these observations are correct, then
there is no need to invoke a planet around 51 Peg to explain the data. Here we
report observations of 51 Peg at a much higher spectral resolution than those
in ref.9, in which we find no evidence for systematic changes in the line
shapes. The data are most consistent with a planetary companion to 51 Peg.Comment: LaTeX, 6 pages, 2 figures. To appear in 8 January 1998 issue of
Natur
Spitzer observations of the Hyades: Circumstellar debris disks at 625 Myr of age
We use the Spitzer Space Telescope to search for infrared excess at 24, 70,
and 160 micron due to debris disks around a sample of 45 FGK-type members of
the Hyades cluster. We supplement our observations with archival 24 and 70
micron Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members
in order to provide robust statistics on the incidence of debris disks at 625
Myr of age an era corresponding to the late heavy bombardment in the Solar
System. We find that none of the 67 FGK-type stars in our sample show evidence
for a debris disk, while 2 out of the 11 A-type stars do so. This difference in
debris disk detection rate is likely to be due to a sensitivity bias in favor
of early-type stars. The fractional disk luminosity, L_dust/L*, of the disks
around the two A-type stars is ~4.0E-5, a level that is below the sensitivity
of our observations toward the FGK-type stars. However, our sensitivity limits
for FGK-type stars are able to exclude, at the 2-sigma level, frequencies
higher than 12% and 5% of disks with L_dust/L* > 1.0E-4 and L_dust/L* > 5.0E-4,
respectively. We also use our sensitivity limits and debris disk models to
constrain the maximum mass of dust, as a function of distance from the stars,
that could remain undetected around our targets.Comment: 33 pages, 11 figures, accepted by Ap
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