119 research outputs found
KIC 4150611: a rare multi-eclipsing quintuple with a hybrid pulsator
We present the results of our analysis of KIC 4150611 (HD 181469) - an
interesting, bright quintuple system that includes a hybrid
Sct/ Dor pulsator. Four periods of eclipses - 94.2, 8.65, 1.52 and 1.43
d - have been observed by the Kepler satellite, and three point sources (A, B,
and C) are seen in high angular resolution images.
From spectroscopic observations made with the HIDES spectrograph attached to
the 1.88-m telescope of the Okayama Astrophysical Observatory (OAO), for the
first time we calculated radial velocities (RVs) of the component B - a pair of
G-type stars - and combined them with Kepler photometry in order to obtain
absolute physical parameters of this pair. We also managed to directly measure
RVs of the pulsator, also for the first time. Additionally, we modelled the
light curves of the 1.52 and 1.43-day pairs, and measured their eclipse timing
variations (ETVs). We also performed relative astrometry and photometry of
three sources seen on the images taken with the NIRC2 camera of the Keck II
telescope. Finally, we compared our results with theoretical isochrones.
The brightest component Aa is the hybrid pulsator, transited every 94.2 days
by a pair of K/M-type stars (Ab1+Ab2), which themselves form a 1.52-day
eclipsing binary. The components Ba and Bb are late G-type stars, forming
another eclipsing pair with a 8.65 day period. Their masses and radii are
M, R for the
primary, and M, R
for the secondary. The remaining period of 1.43 days is possibly related to a
faint third star C, which itself is most likely a background object. The
system's properties are well-represented by a 35 Myr isochrone. There are also
hints of additional bodies in the system.Comment: 14 pages, 15 figures, 7 tables, to appear in A&A, abstract modified
in order to fit the arXiv limi
Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars
We discuss two multiple star systems that host known exoplanets: HD 2638 and
30 Ari B. Adaptive optics imagery revealed an additional stellar companion to
both stars. We collected multi-epoch images of the systems with Robo-AO and the
PALM-3000 adaptive optics systems at Palomar Observatory and provide relative
photometry and astrometry. The astrometry indicates that the companions share
common proper motion with their respective primaries. Both of the new
companions have projected separations less than 30 AU from the exoplanet host
star. Using the projected separations to compute orbital periods of the new
stellar companions, HD 2638 has a period of 130 yrs and 30 Ari B has a period
of 80 years. Previous studies have shown that the true period is most likely
within a factor of three of these estimated values. The additional component to
the 30 Ari makes it the second confirmed quadruple system known to host an
exoplanet. HD 2638 hosts a hot Jupiter and the discovery of a new companion
strengthens the connection between hot Jupiters and binary stars. We place the
systems on a color-magnitude diagram and derive masses for the companions which
turn out to be roughly 0.5 solar mass stars.Comment: Accepted to Astronomical Journal, 16 pages, 5 Figure
Ground-layer wavefront reconstruction from multiple natural guide stars
Observational tests of ground layer wavefront recovery have been made in open
loop using a constellation of four natural guide stars at the 1.55 m Kuiper
telescope in Arizona. Such tests explore the effectiveness of wide-field seeing
improvement by correction of low-lying atmospheric turbulence with ground-layer
adaptive optics (GLAO). The wavefronts from the four stars were measured
simultaneously on a Shack-Hartmann wavefront sensor (WFS). The WFS placed a 5 x
5 array of square subapertures across the pupil of the telescope, allowing for
wavefront reconstruction up to the fifth radial Zernike order. We find that the
wavefront aberration in each star can be roughly halved by subtracting the
average of the wavefronts from the other three stars. Wavefront correction on
this basis leads to a reduction in width of the seeing-limited stellar image by
up to a factor of 3, with image sharpening effective from the visible to near
infrared wavelengths over a field of at least 2 arc minutes. We conclude that
GLAO correction will be a valuable tool that can increase resolution and
spectrographic throughput across a broad range of seeing-limited observations.Comment: 25 pages, 8 figures, to be published in Astrophys.
Reconnaissance of the HR 8799 Exosolar System. I. Near-infrared Spectroscopy
We obtained spectra in the wavelength range λ = 995-1769 nm of all four known planets orbiting the star HR 8799. Using the suite of instrumentation known as Project 1640 on the Palomar 5 m Hale Telescope, we acquired data at two epochs. This allowed for multiple imaging detections of the companions and multiple extractions of low-resolution (R ~ 35) spectra. Data reduction employed two different methods of speckle suppression and spectrum extraction, both yielding results that agree. The spectra do not directly correspond to those of any known objects, although similarities with L and T dwarfs are present, as well as some characteristics similar to planets such as Saturn. We tentatively identify the presence of CH_4 along with NH_3 and/or C_2H_2, and possibly CO_2 or HCN in varying amounts in each component of the system. Other studies suggested red colors for these faint companions, and our data confirm those observations. Cloudy models, based on previous photometric observations, may provide the best explanation for the new data presented here. Notable in our data is that these presumably co-eval objects of similar luminosity have significantly different spectra; the diversity of planets may be greater than previously thought. The techniques and methods employed in this paper represent a new capability to observe and rapidly characterize exoplanetary systems in a routine manner over a broad range of planet masses and separations. These are the first simultaneous spectroscopic observations of multiple planets in a planetary system other than our own
Robo-AO and SOAR High-Resolution Surveys of Exoplanet Hosting Stars
In the past decade, space-based transit surveys have delivered thousands of potential planet-hosting systems. Each of these needs to be vetted and characterized using follow-up high-resolution imaging. We perform comprehensive imaging surveys of the candidate exoplanets detected by the Kepler and TESS missions using the fully autonomous Robo-AO system and the largely autonomous SOAR speckle imaging system. The surveys yielded hundreds of previously unknown close binary systems hosting exoplanets and resulted in verification of hundreds of exoplanet systems. Evidence of the interaction between binary stars and planetary systems was also detected, including a deep deficit of planets in close binary systems
Laser Guide Stars for Extremely Large Telescopes: Efficient Shack-Hartmann Wavefront Sensor Design using Weighted center-of-gravity algorithm
Over the last few years increasing consideration has been given to the study
of Laser Guide Stars (LGS) for the measurement of the disturbance introduced by
the atmosphere in optical and near-infrared astronomical observations from the
ground. A possible method for the generation of a LGS is the excitation of the
Sodium layer in the upper atmosphere at approximately 90 km of altitude. Since
the Sodium layer is approximately 10 km thick, the artificial reference source
looks elongated, especially when observed from the edge of a large aperture.
The spot elongation strongly limits the performance of the most common
wavefront sensors. The centroiding accuracy in a Shack-Hartmann wavefront
sensor, for instance, decreases proportionally to the elongation (in a photon
noise dominated regime). To compensate for this effect a straightforward
solution is to increase the laser power, i.e. to increase the number of
detected photons per subaperture. The scope of the work presented in this paper
is twofold: an analysis of the performance of the Weighted Center of Gravity
algorithm for centroiding with elongated spots and the determination of the
required number of photons to achieve a certain average wavefront error over
the telescope aperture.Comment: 10 pages, 14 figure
Five Planets Transiting a Ninth Magnitude Star
The Kepler mission has revealed a great diversity of planetary systems and
architectures, but most of the planets discovered by Kepler orbit faint stars.
Using new data from the K2 mission, we present the discovery of a five planet
system transiting a bright (V = 8.9, K = 7.7) star called HIP 41378. HIP 41378
is a slightly metal-poor late F-type star with moderate rotation (v sin(i) = 7
km/s) and lies at a distance of 116 +/- 18 from Earth. We find that HIP 41378
hosts two sub-Neptune sized planets orbiting 3.5% outside a 2:1 period
commensurability in 15.6 and 31.7 day orbits. In addition, we detect three
planets which each transit once during the 75 days spanned by K2 observations.
One planet is Neptune sized in a likely ~160 day orbit, one is sub-Saturn sized
likely in a ~130 day orbit, and one is a Jupiter sized planet in a likely ~1
year orbit. We show that these estimates for the orbital periods can be made
more precise by taking into account dynamical stability considerations. We also
calculate the distribution of stellar reflex velocities expected for this
system, and show that it provides a good target for future radial velocity
observations. If a precise orbital period can be determined for the outer
Jovian planet through future observations, it will be an excellent candidate
for follow-up transit observations to study its atmosphere and measure its
oblateness.Comment: Accepted by ApJL. 12 pages, 6 figures, 2 table
First tests of wavefront sensing with a constellation of laser guide beacons
Adaptive optics to correct current telescopes over wide fields, or future
very large telescopes over even narrow fields, will require real-time wavefront
measurements made with a constellation of laser beacons. Here we report the
first such measurements, made at the 6.5 m MMT with five Rayleigh beacons in a
2 arcmin pentagon. Each beacon is made with a pulsed beam at 532 nm, of 4 W at
the exit pupil of the projector. The return is range-gated from 20-29 km and
recorded at 53 Hz by a 36-element Shack-Hartmann sensor. Wavefronts derived
from the beacons are compared with simultaneous wavefronts obtained for
individual natural stars within or near the constellation. Observations were
made in seeing averaging 1.0 arcsec with 2/3 of the aberration measured to be
from a ground layer of mean height 380 m. Under these conditions, subtraction
of the simple instantaneous average of the five beacon wavefronts from the
stellar wavefronts yielded a 40% rms reduction in the measured modes of the
distortion over a 2 arcmin field. We discuss the use of multiple Rayleigh
beacons as an alternative to single sodium beacons on 8 m telescopes, and the
impact of the new work on the design of a multi-sodium beacon system for the 25
m Giant Magellan Telescope.Comment: 25 pages, 7 figures, uses aastex.cls, to be published in the
Astrophys.
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