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ABSTRACT: We present Herschel spatially resolved images of the debris disc orbiting the
subgiant Kappa CrB. Not only are these the first resolved images of a debris
disc orbiting a subgiant, but Kappa CrB is a rare example of an intermediate
mass star where a detailed study of the structure of the planetary system can
be made, including both planets and planetesimal belt(s). The only way to
discover planets around such stars using the radial velocity technique is to
observe 'retired' A stars, which are cooler and slower rotators compared to
their main-sequence counterparts. A planetary companion has already been
detected orbiting the subgiant Kappa CrB, with revised parameters of m sin i =
2.1MJ and apl = 2.8AU (Johnson et al. 2008a). We present additional Keck I
HIRES radial velocity measurements that provide evidence for a second planetary
companion, alongside Keck II AO imaging that places an upper limit on the mass
of this companion. Modelling of our Herschel images shows that the dust is
broadly distributed, but cannot distinguish between a single wide belt (from 20
to 220AU) or two narrow dust belts (at around 40 and 165AU). Given the
existence of a second planetary companion beyond approximately 3AU it is
possible that the absence of dust within approximately 20AU is caused by
dynamical depletion, although the observations are not inconsistent with
depletion of these regions by collisional erosion, which occurs at higher rates
closer to the star.
02/2013;
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Hannah Broekhoven-Fiene,
Brenda C. Matthews,
Grant M. Kennedy,
Mark Booth,
Bruce Sibthorpe,
Samantha M. Lawler,
J. J. Kavelaars,
Mark C. Wyatt,
Chenruo Qi,
Alice Koning, Kate Y. L. Su,
George H. Rieke,
David J. Wilner,
Jane S. Greaves,
for the DEBRIS collaboration
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ABSTRACT: We present observations of the debris disk around gamma Doradus, an F1V star,
from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free
Reconnaissance in the Infrared/Submillimetre). The disk is well-resolved at 70,
100 and 160 micron, resolved along its major axis at 250 micron, detected but
not resolved at 350 micron, and confused with a background source at 500
micron. It is one of our best resolved targets and we find it to have a
radially broad dust distribution. The modelling of the resolved images cannot
distinguish between two configurations: an arrangement of a warm inner ring at
several AU (best-fit 4 AU) and a cool outer belt extending from ~55 to 400 AU
or an arrangement of two cool, narrow rings at ~70 AU and ~190 AU. This
suggests that any configuration between these two is also possible. Both models
have a total fractional luminosity of ~10^{-5} and are consistent with the disk
being aligned with the stellar equator. The inner edge of either possible
configuration suggests that the most likely region to find planets in this
system would be within ~55 AU of the star. A transient event is not needed to
explain the warm dust's fractional luminosity.
12/2012;
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Mark Booth,
Grant Kennedy,
Bruce Sibthorpe,
Brenda C. Matthews,
Mark C. Wyatt,
Gaspard Duchêne,
J. J. Kavelaars,
David Rodriguez,
Jane S. Greaves,
Alice Koning,
Laura Vican,
George H. Rieke, Kate Y. L. Su,
Amaya Moro-Martín,
Paul Kalas
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ABSTRACT: The majority of debris discs discovered so far have only been detected
through infrared excess emission above stellar photospheres. While disc
properties can be inferred from unresolved photometry alone under various
assumptions for the physical properties of dust grains, there is a degeneracy
between disc radius and dust temperature that depends on the grain size
distribution and optical properties. By resolving the disc we can measure the
actual location of the dust. The launch of Herschel, with an angular resolution
superior to previous far-infrared telescopes, allows us to spatially resolve
more discs and locate the dust directly. Here we present the nine resolved
discs around A stars between 20 and 40 pc observed by the DEBRIS survey. We use
these data to investigate the disc radii by fitting narrow ring models to
images at 70, 100 and 160 {\mu}m and by fitting blackbodies to full spectral
energy distributions. We do this with the aim of finding an improved way of
estimating disc radii for unresolved systems. The ratio between the resolved
and blackbody radii varies between 1 and 2.5. This ratio is inversely
correlated with luminosity and any remaining discrepancies are most likely
explained by differences to the minimum size of grain in the size distribution
or differences in composition. We find that three of the systems are well fit
by a narrow ring, two systems are borderline cases and the other four likely
require wider or multiple rings to fully explain the observations, reflecting
the diversity of planetary systems.
10/2012;
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ABSTRACT: We have obtained Spitzer Space Telescope Multiband Imaging Photometer for
Spitzer (MIPS) 24 {\mu}m and 70 {\mu}m observations of 215 nearby, Hipparcos B-
and A-type common proper motion single and binary systems in the nearest OB
association, Scorpius-Centaurus. Combining our MIPS observations with those of
other ScoCen stars in the literature, we estimate 24 {\mu}m B+A-type disk
fractions of 17/67 (25+6%), 36/131 (27+4%), and 23/95 (24+5%) for Upper
Scorpius (\sim11 Myr), Upper Centaurus Lupus (\sim15 Myr), and Lower Centaurus
Crux (\sim17 Myr), respectively, somewhat smaller disk fractions than
previously obtained for F- and G-type members. We confirm previous IRAS excess
detections and present new discoveries of 51 protoplanetary and debris disk
systems, with fractional infrared luminosities ranging from LIR/L\ast = 1e-6 to
1e-2 and grain temperatures ranging from Tgr = 40 - 300 K. In addition, we
confirm that the 24 {\mu}m and 70 {\mu}m excesses (or fractional infrared
luminosities) around B+A type stars are smaller than those measured toward F+G
type stars and hypothesize that the observed disk property dependence on
stellar mass may be the result of a higher stellar companion fraction around B-
and A-type stars at 10 - 200 AU and/or the presence of Jupiter-mass companions
in the disks around F- and G- type stars. Finally, we note that the majority of
the ScoCen 24 {\mu}m excess sources also possess 12 {\mu}m excess, indicating
that Earth-like planets may be forming via collisions in the terrestrial planet
zone at \sim10 - 100 Myr.
07/2012;
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ABSTRACT: Debris disks with extremely large infrared excesses (fractional luminosities
$> 10^{-2}$) are rare. Those with ages between 30 and 130 Myr are of interest
because their evolution has progressed well beyond that of protoplanetary disks
(which dissipate with a timescale of order 3 Myr), yet they represent a period
when dynamical models suggest that terrestrial planet building may still be
progressing through large, violent collisions that could yield large amounts of
debris and large infrared excesses. For example, our Moon was formed through a
violent collision of two large proto-planets during this age range. We report
two disks around the solar-like stars ID8 and HD 23514 in this age range where
the 24 {\mu}m infrared excesses vary on timescales of a few years, even though
the stars are not variable in the optical. Variations this rapid are difficult
to understand if the debris is produced by collisional cascades, as it is for
most debris disks. It is possible that the debris in these two systems arises
in part from condensates from silicate-rich vapor produced in a series of
violent collisions among relatively large bodies. If their evolution is rapid,
the rate of detection of extreme excesses would indicate that major collisions
may be relatively common in this age range.
05/2012;
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ABSTRACT: We obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 μm and 70 μm observations of 182 nearby, Hipparcos F- and G-type common proper motion single and binary systems in the nearest OB association, Scorpius-Centaurus. We also obtained Magellan/MIKE R ~ 50,000 visual spectra at 3500-10500 Å for 181 candidate ScoCen stars in single and binary systems. Combining our MIPS observations with those of other ScoCen stars in the literature, we estimate 24 μm F+G-type disk fractions of 9/27 (33% ± 11%), 21/67 (31% ± 7%), and 25/71 (35% ± 7%) for Upper Scorpius (~10 Myr), Upper Centaurus Lupus (~15 Myr), and Lower Centaurus Crux (~17 Myr), respectively. We confirm previous IRAS and MIPS excess detections and present new discoveries of 41 protoplanetary and debris disk systems, with fractional infrared luminosities ranging from L IR/L * = 10–5 to 10–2 and grain temperatures ranging from T gr = 40-300 K. We searched for an increase in 24 μm excess at an age of 15-20 Myr, consistent with the onset of debris production predicted by coagulation N-body simulations of outer planetary systems. We found such an increase around 1.5 M ☉ stars but discovered a decrease in the 24 μm excess around 1.0 M ☉ stars. We additionally discovered that the 24 μm excess around 1.0 M ☉ stars is larger than predicted by self-stirred models. Finally, we found a weak anti-correlation between fractional infrared luminosity (L IR/L *) and chromospheric activity (R'HK), that may be the result of differences in stellar properties, such as mass, luminosity, and/or winds.
The Astrophysical Journal 08/2011; 738(2):122. · 6.02 Impact Factor
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ABSTRACT: We combine nulling interferometry at 10 μm using the MMT and Keck Telescopes with spectroscopy, imaging, and photometry from 3 to 100 μm using Spitzer to study the debris disk around β Leo over a broad range of spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured the close binary star o Leo with both Keck and MMT interferometers to verify our procedures with these instruments. The β Leo debris system has a complex structure: (1) relatively little material within 1 AU; (2) an inner component with a color temperature of ~600 K, fitted by a dusty ring from about 2–3 AU; and (3) a second component with a color temperature of ~120 K fitted by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike many other A-type stars with debris disks, β Leo lacks a dominant outer belt near 100 AU.
The Astrophysical Journal 11/2010; · 6.02 Impact Factor
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ABSTRACT: We combine nulling interferometry at 10 {\mu}m using the MMT and Keck Telescopes with spectroscopy, imaging, and photometry from 3 to 100 {\mu}m using Spitzer to study the debris disk around {\beta} Leo over a broad range of spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured the close binary star o Leo with both Keck and MMT interferometers to verify our procedures with these instruments. The {\beta} Leo debris system has a complex structure: 1.) relatively little material within 1 AU; 2.) an inner component with a color temperature of ~600 K, fitted by a dusty ring from about 2 to 3 AU; and 3.) a second component with a color temperature of ~120 K fitted by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike many other A-type stars with debris disks, {\beta} Leo lacks a dominant outer belt near 100 AU. Comment: 14 page body, 3 page appendix, 15 figures
09/2010;
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ABSTRACT: We consider the limiting case for orbital stability of the companions to HR 8799. This case is only consistent with ages for the system of ~100 Myr, not with the 1 Gyr age proposed from astroseismology. The discrepancy probably arises because the inclination of the star is smaller than assumed in analyzing the astroseismology data. Given this young age, the best estimates of the companion masses place them by a small margin on the planet side of the division between planets and brown dwarfs. Comment: 4 pages, 2 figures, accepted by ApJ Letters
08/2010;
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ABSTRACT: In addition to the Sun, six other stars are known to harbor multiple planets and debris disks: HD 69830, HD 38529, HD 128311, HD 202206, HD 82943, and HR 8799. In this paper, we set constraints on the location of the dust-producing planetesimals around the latter four systems. We use a radiative transfer model to analyze the spectral energy distributions of the dust disks (including two new Spitzer IRS spectra presented in this paper), and a dynamical model to assess the long-term stability of the planetesimals' orbits. As members of a small group of stars that show evidence of harboring a multiple planets and planetesimals, their study can help us learn about the diversity of planetary systems.
The Astrophysical Journal 06/2010; 717(2):1123. · 6.02 Impact Factor
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ABSTRACT: In addition to the Sun, six other stars are known to harbor multiple planets and debris disks: HD 69830, HD 38529, HD 128311, HD 202206, HD 82943 and HR 8799. In this paper we set constraints on the location of the dust-producing planetesimals around the latter four systems. We use a radiative transfer model to analyze the spectral energy distributions of the dust disks (including two new Spitzer IRS spectra presented in this paper), and a dynamical model to assess the long-term stability of the planetesimals' orbits. As members of a small group of stars that show evidence of harboring a multiple planets and planetesimals, their study can help us learn about the diversity of planetary systems. Comment: Accepted by ApJ (18 pages, 19 figures - one figure added from last submission)
05/2010;
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ABSTRACT: We present the results from a survey of NGC 2244 from 3.6 to 24 μm with the Spitzer Space Telescope. The 24 μm-8 μm-3.6 μm color composite image of the region shows that the central cavity surrounding the multiple O and B stars of NGC 2244 contains a large amount of cool dust visible only at 24 μm. Our survey gives a detailed look at disk survivability within the hot-star-dominated environment in this cavity. Using mid-infrared two-color diagrams ([3.6] - [4.5] vs. [5.8] - [8.0]), we identified 337 class II and 25 class I objects out of 1084 objects detected in all four of these bands with photometric uncertainty better than 10%. Including the 24 μm data, we found 213 class II and 20 class I sources out of 279 stars also detected at this latter band. The center of the class II density contours is in very good agreement with the center of the cluster detected in the 2MASS images. We studied the distribution of the class II sources relative to the O stars and found that the effect of high-mass stars on the circumstellar disks is significant only in their immediate vicinity.
The Astrophysical Journal 12/2008; 660(2):1532. · 6.02 Impact Factor
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ABSTRACT: We present 24 μm images of three protoplanetary disks being photoevaporated around high-mass O-type stars. These objects have "cometary" structure where the dust pulled away from the disk by the photoevaporating flow is forced away from the O star by photon pressure on the dust and heating and ionization of the gas. Models of the 24 and 8 μm brightness profiles agree with this hypothesis. These models show that the mass-loss rate needed to sustain such a configuration is in agreement with or somewhat less than the theoretical predictions for the photoevaporation process.
The Astrophysical Journal 12/2008; 650(1):L83. · 6.02 Impact Factor
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Nadya Gorlova,
Deborah L. Padgett,
George H. Rieke,
James Muzerolle,
Jane E. Morrison,
Karl D. Gordon,
Chad W. Engelbracht,
Dean C. Hines,
Joannah C. Hinz,
Alberto Noriega-Crespo,
Luisa Rebull,
John A. Stansberry,
Karl R. Stapelfeldt, Kate Y. L. Su,
and Erick T. Young
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ABSTRACT: Sixty-three members of the 100 Myr old open cluster M47 (NGC 2422) have been detected at 24 μm with the Spitzer Space Telescope. The Be star V 378 Pup shows an excess both in the near-infrared and at 24 μm (K - [24] = 2.4 mag), probably due to free-free emission from the gaseous envelope. Seven other early-type stars show smaller excesses, K - [24] = 0.6-0.9. Among late-type stars, two show large excesses: P922, a K1 V star with K - [24] = 1.08 ± 0.11, and P1121, an F9 V star with K - [24] = 3.72 ± 0.02. P1121 is the first known main-sequence star showing an excess comparable to that of β Pic, which may indicate the presence of an exceptionally massive debris disk. It is possible that a major planetesimal collision has occurred in this system, consistent with the few hundred Myr timescales estimated for the clearing of the solar system.
The Astrophysical Journal Supplement Series 12/2008; 154(1):448. · 13.46 Impact Factor
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ABSTRACT: We present 24 micron Spitzer/MIPS photometric observations of the ~50 Myr open cluster IC 2391. Thirty-four cluster members ranging in spectral type from B3-M5 were observed in the central square degree of the cluster. Excesses indicative of debris disks were discovered around 1 A star, 6 FGK stars, and possibly 1 M dwarf. For the cluster members observed to their photospheric limit, we find a debris disk frequency of 10 (-3,+17)% for B-A stars and 31 (-9,+13)% for FGK stars using a 15% relative excess threshold. Relative to a model of decaying excess frequency, the frequency of debris disks around A-type stars appears marginally low for the cluster's age while that of FGK stars appears consistent. Scenarios that may qualitatively explain this result are examined. We conclude that planetesimal activity in the terrestrial region of FGK stars is common in the first ~50 Myr and decays on timescales of ~100 Myr. Despite luminosity differences, debris disk evolution does not appear to depend strongly on stellar mass.
10/2006;
