arXiv subjects

J. Patience

Publications and source records attributed to J. Patience.

34 records · Page 2Linked to original sources

arXiv2013

Sub-millimeter observations of IRAS and WISE debris disk candidates

A set of six debris disk candidates identified with IRAS or WISE excesses were observed at either 350 um or 450 um with the CSO. Five of the targets - HIP 51658, HIP 68160, HIP 73512, HIP 76375, and HIP 112460 - have among the largest measured excess emission from cold dust from IRAS in the 25-100 um bands. Single temperature blackbody fits to the excess dust emission of these sources predict 350-450 um fluxes above 240 mJy. The final target - HIP 73165 - exhibits weak excess emission above the stellar photosphere from WISE measurements at 22 um, indicative of a population of warm circumstellar dust. None of the six targets were detected, with 3 sigma upper limits ranging from 51-239 mJy. These limits are significantly below the expected fluxes from SED fitting. Two potential causes of the null detections were explored - companion stars and contamination. To investigate the possible influence of companion stars, imaging data were analyzed from new AO data from the MMT and archival HST, NIRI, and POSS/2MASS data. The images are sensitive to all stellar companions beyond a radius of 1-94 AU. One target is identified as a binary system, but with a separation too large to impact the disk. While the gravitational effects of a companion do not appear to provide an explanation for the submm upper limits, the majority of the IRAS excess targets show evidence for contaminating sources, based on investigation of higher resolution WISE and archival Spitzer and Herschel images. Finally, the exploratory submm measurements of the WISE excess source suggest that the hot dust present around these targets is not matched by a comparable population of colder, outer dust. More extensive and more sensitive Herschel observations of WISE excess sources will build upon this initial example to further define the characteristics of warm debris disks sources.

astro-ph.SR↗

arXiv2012

The International Deep Planet Survey I. The frequency of wide-orbit massive planets around A-stars

Breakthrough direct detections of planetary companions orbiting A-type stars confirm the existence of massive planets at relatively large separations, but dedicated surveys are required to estimate the frequency of similar planetary systems. To measure the first estimation of the giant exoplanetary systems frequency at large orbital separation around A-stars, we have conducted a deep-imaging survey of young (8-400 Myr), nearby (19-84 pc) A- and F-stars to search for substellar companions in the 10-300 AU range. The sample of 42 stars combines all A-stars observed in previous AO planet search surveys reported in the literature with new AO observations from VLT/NaCo and Gemini/NIRI. It represents an initial subset of the International Deep Planet Survey (IDPS) sample of stars covering M- to B-stars. The data were obtained with diffraction-limited observations in H- and Ks-band combined with angular differential imaging to suppress the speckle noise of the central stars, resulting in typical 5-sigma detection limits in magnitude difference of 12 mag at 1", 14 mag at 2" and 16 mag at 5" which is sufficient to detect massive planets. A detailed statistical analysis of the survey results is performed using Monte Carlo simulations. Considering the planet detections, we estimate the fraction of A-stars having at least one massive planet (3-14 MJup) in the range 5-320 AU to be inside 5.9-18.8% at 68% confidence, assuming a flat distribution for the mass of the planets. By comparison, the brown dwarf (15-75 MJup) frequency for the sample is 2.0-8.9% at 68% confidence in the range 5-320 AU. Assuming power law distributions for the mass and semimajor axis of the planet population, the AO data are consistent with a declining number of massive planets with increasing orbital radius which is distinct from the rising slope inferred from radial velocity (RV) surveys around evolved A-stars.

astro-ph.EP↗

arXiv2012

Spectroscopy across the brown dwarf/planetary mass boundary - I. Near-infrared JHK spectra

With a uniform VLT SINFONI data set of nine targets, we have developed an empirical grid of J,H,K spectra of the atmospheres of objects estimated to have very low substellar masses of \sim5-20 MJup and young ages of \sim1-50 Myr. Most of the targets are companions, objects which are especially valuable for comparison with atmosphere and evolutionary models, as they present rare cases in which the age is accurately known from the primary. Based on the sample youth, all objects are expected to have low surface gravity, and this study investigates the critical early phases of the evolution of substellar objects. The spectra are compared with grids of five different theoretical atmosphere models. This analysis represents the first systematic model comparison with infrared spectra of young brown dwarfs. The fits to the full JHK spectra of each object result in a range of best fit effective temperatures of +/-150-300K whether or not the full model grid or a subset restricted to lower log(g) values is used. This effective temperature range is significantly larger than the uncertainty typically assigned when using a single model grid. Fits to a single wavelength band can vary by up to 1000K using the different models. Since the overall shape of these spectra is governed more by the temperature than surface gravity, unconstrained model fits did not find matches with low surface gravity or a trend in log(g) with age. This suggests that empirical comparison with spectra of unambiguously young objects targets (such as these SINFONI data) may be the most reliable method to search for indications of low surface gravity and youth. For two targets, the SINFONI data are a second epoch and the data show no variations in morphology over time. The analysis of two other targets, AB Pic B and CT Cha B, suggests that these objects may have lower temperatures, and consequently lower masses, than previously estimated.

astro-ph.EP↗

arXiv2011

Spatially resolved submm imaging of the HR 8799 debris disk

Dynamical interactions between planets and debris disks may sculpt the disk structure and impact planetary orbits, but only a few systems with both imaged planets and spatially resolved debris disks are known. With the Caltech Submm Observatory (CSO), we have observed the HR 8799 debris disk at 350μm. The 350μm map is the first spatially resolved measurement of the debris disk encircling the HR 8799 planetary system at this wavelength. Both the flux and size of the emission are consistent with a Kuiper belt of dust extending from ~100-300 AU. Although the resolution of the current map is limited, the map shows an indication of offset asymmetric emission, and several scenarios for this possibility are explored with radiative transfer calculations of a star-disk system and N-body numerical simulations of planet-disk interactions with parameters representative of the HR 8799 system.

astro-ph.EP↗

arXiv2011

CO(1-0) imaging of M51 with CARMA and NRO45

We report the CO(J=1-0) observations of M51 using both the Combined Array for Research in Millimeter Astronomy (CARMA) and the Nobeyama 45m telescope (NRO45). We describe a procedure for the combination of interferometer and single-dish data. In particular, we discuss (1) the joint imaging and deconvolution of heterogeneous data, (2) the weighting scheme based on the root-mean-square (RMS) noise in the maps, (3) the sensitivity and uv-coverage requirements, and (4) the flux recovery of a combined map. We generate visibilities from the single-dish map and calculate the noise of each visibility based on the RMS noise. Our weighting scheme, though it is applied to discrete visibilities in this paper, is applicable to grids in uv-space, and this scheme may advance in future software development. For a realistic amount of observing time, the sensitivities of the NRO45 and CARMA visibility data sets are best matched by using the single dish baselines only up to 4-6 kilo-lambda (about 1/4-1/3 of the dish diameter). The synthesized beam size is determined to conserve the flux between synthesized beam and convolution beam. The superior uv-coverage provided by the combination of CARMA long baseline data with 15 antennas and NRO45 short spacing data results in the high image fidelity, which is evidenced by the excellent overlap between even the faint CO emission and dust lanes in an optical HST image and PAH emission in an Spitzer 8 micron image.

astro-ph.IM↗

arXiv2009

Dynamically Driven Evolution of the Interstellar Medium in M51

We report the highest-fidelity observations of the spiral galaxy M51 in CO emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis the large-scale galactic structure and dynamics. The most massive GMCs (so-called GMAs) are first assembled and then broken up as the gas flow through the spiral arms. The GMAs and their H2 molecules are not fully dissociated into atomic gas as predicted in stellar feedback scenarios, but are fragmented into smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as the chains of GMCs that emerge from the spiral arms into interarm regions. The kinematic shear within the spiral arms is sufficient to unbind the GMAs against self-gravity. We conclude that the evolution of GMCs is driven by large-scale galactic dynamics --their coagulation into GMAs is due to spiral arm streaming motions upon entering the arms, followed by fragmentation due to shear as they leave the arms on the downstream side. In M51, the majority of the gas remains molecular from arm entry through the inter-arm region and into the next spiral arm passage.

astro-ph.CO↗

arXiv2008

Direct Imaging of Multiple Planets Orbiting the Star HR 8799

Direct imaging of exoplanetary systems is a powerful technique that can reveal Jupiter-like planets in wide orbits, can enable detailed characterization of planetary atmospheres, and is a key step towards imaging Earth-like planets. Imaging detections are challenging due to the combined effect of small angular separation and large luminosity contrast between a planet and its host star. High-contrast observations with the Keck and Gemini telescopes have revealed three planets orbiting the star HR 8799, with projected separations of 24, 38, and 68 astronomical units. Multi-epoch data show counter-clockwise orbital motion for all three imaged planets. The low luminosity of the companions and the estimated age of the system imply planetary masses between 5 and 13 times that of Jupiter. This system resembles a scaled-up version of the outer portion of our Solar System.

astro-ph↗

arXiv2008

The Evolution of Circumstellar Disks in Ophiuchus Binaries

Four Ophiuchus binaries, two Class I systems and two Class II systems, with separations of ~450-1100 AU, were observed with the Owens Valley Radio Observatory (OVRO) millimeter interferometer. In each system, the 3 mm continuum maps show dust emission at the location of the primary star, but no emission at the position of the secondary. This result is different from observations of less evolved Class 0 binaries, in which dust emission is detected from both sources. The nondetection of secondary disks is, however, similar to the dust distribution seen in wide Class II Taurus binaries. The combined OVRO results from the Ophiuchus and Taurus binaries suggest that secondary disk masses are significantly lower than primary disk masses by the Class II stage, with initial evidence that massive secondary disks are reduced by the Class I stage. Although some of the secondaries retain hot inner disk material, the early dissipation of massive outer disks may negatively impact planet formation around secondary stars. Masses for the circumprimary disks are within the range of masses measured for disks around single T Tauri stars and, in some cases, larger than the minimum mass solar nebula. More massive primary disks are predicted by several formation models and are broadly consistent with the observations. Combining the 3 mm data with previous 1.3 mm observations, the dust opacity power-law index for each primary disk is estimated. The opacity index values are all less than the scaling for interstellar dust, possibly indicating grain growth within the circumprimary disks.

astro-ph↗

arXiv2008

Optical interferometric observations of Theta 1 Orionis C from NPOI and implications for the system orbit

With the Navy Prototype Optical Interferometer (NPOI), the binary system Theta 1 Orionis C, the most massive member of the Trapezium, was spatially resolved over a time period extending from February 2006 to March 2007. The data show significant orbital motion over the 14 months, and, after combining the NPOI data with previous measurements of the system from the literature, the observations span 10 years of the orbit. Our results indicate that the secondary did not experience an unusually close periastron passage this year, in contradiction to the prediction of a recently published, highly eccentric ~11 year orbit. Future observations of this source will be required to improve the orbital solution. Possible implications of the results in terms of system distance are discussed, although a main conclusion of this work is that a definitive orbit solution will require more time to obtain sufficient phase coverage, and that the interaction effects expected at periastron did not occur in 2007.

astro-ph↗

arXiv2005

Low-mass companions to Hyades stars

It is now well established that a large fraction of the low-mass stars are binaries or higher order multiples. Similarly a sizable fraction have giant planets. In contrast to these, the situation for brown dwarf companions is complicated: While close systems seem to be extremely rare, wide systems are possibly more common. In this paper, we present new results on a survey for low-mass companions in the Hyades. After measuring precisely the radial velocity of 98 Hyades dwarf stars for 5 years, we have selected all stars that show low-amplitude long-period trends. With AO-observations of these 14 stars we found companion candidates around nine of them, where one star has two companions. The two companions of HIP 16548 have masses between 0.07 to 0.08 Mo, and are thus either brown dwarfs or very low mass stars. In the case of HAN 172 we found a companion with a mass between 0.08 to 0.10 Mo, which is again between a star and a brown dwarf. The other seven stars all have stellar companions. In two additional cases, the RV-variations are presumably caused by stellar activity, and in another case the companion could be a short-period binary. The images of the remaining two stars are slightly elongated, which might imply that even these are binaries. Because at least 12 of the 14 stars showing low-amplitude RV trends turn out to have companions with a mass greater than 70 MJupiter, or are just active, we finally estimate the number of companions with masses between 10 MJupiter and 70 MJupiter within 8 AU of the host stars in the Hyades as less equal 2%.

astro-ph↗

arXiv2003

HD 199143 and HD 358623: Two Recently Identified Members of the Beta Pictoris Moving Group

HD 199143 and HD 358623 (BD-17 6128) are two sets of binary stars which are physically associated and 48 pc from Earth. We present heliocentric radial velocities and high lithium abundances which establish these stars as members of the 12 Myr-old Beta Pictoris Moving Group. We also present mid-IR photometric measurements which show no firm evidence for warm dust around all four stars.

astro-ph↗

arXiv2002

Stellar Companions to Stars with Planets

A combination of high-resolution and wide-field imaging reveals two binary stars and one triple star system among the sample of the first 11 stars with planets detected by radial velocity variations. High resolution speckle or adaptive optics (AO) data probe subarcsecond scales down to the diffraction limit of the Keck 10-m or Lick 3-m, and direct images or AO images are sensitive to a wider field, extending to 10" or 38", depending upon the camera. One of the binary systems -- HD 114762 -- was not previously known to be a spatially resolved multiple system; additional data taken with the combination of Keck adaptive optics and NIRSPEC are used to characterize the new companion. The second binary system -- Tau Boo -- was a known multiple with two conflicting orbital solutions; the current data will help constrain the discrepant estimates of periastron time and separation. Another target -- 16 Cyg B -- was a known common proper motion binary, but the current data resolve a new third component, close to the wide companion 16 Cyg A. Both the HD 114762 and 16 Cyg B systems harbor planets in eccentric orbits, while the Tau Boo binary contains an extremely close planet in a tidally-circularized orbit. Although the sample is currently small, the proportion of binary systems is comparable to that measured in the field over a similar separation range. Incorporating the null result from another companion search project lowers the overall fraction of planets in binary systems, but the detections in our survey reveal that planets can form in binaries separated by less than 50 AU.

astro-ph↗

arXiv2001

A High Angular Resolution Multiplicity Survey of the Open Clusters alpha Persei and Praesepe

Two hundred and forty-two members of the Praesepe and alpha Persei clusters ranging from B (~5Msun) to early-M (~0.5 Msun) have been surveyed with high angular resolution imaging. The 39 binary and 1 quadruple systems detected encompass separations from 0".053 to 7".28; 28 of the systems are new detections and there are 9 candidate substellar companions. The main results from the survey are: * Over the projected separation range of 26-581 AU and magnitude differences of DeltaK < 4.0 mag, the companion star fraction (CSF) for alpha Persei is 0.09 +/- 0.03 and for Praesepe is 0.10 +/- 0.03. This fraction is consistent with the field G-dwarf value, implying that there is not a systematic decline in multiplicity with age on timescales of at 4 +1/-1.5 AU, significantly smaller value than both the field G-dwarf and the nearby T Tauri distributions. A simple population synthesis model suggests that the G-dwarf binary population is a combination of ~30% dark cloud and ~70% giant molecular cloud systems. * An exploration of the binary star properties reveals a cluster CSF that increases with decreasing target mass and a cluster mass ratio distribution that rises more sharply for higher mass stars, but is independent of binary separation. These observational trends are consistent with several models of capture in small clusters and simulations of accretion following fragmentation in a cluster environment. * Among the cluster A stars, there is a higher fraction of binaries in the subset with X-ray detections, consistent with the hypothesis that lower mass companions are the true source of X-ray emission. * In alpha Persei, the rotational velocities for solar-type binaries with separations less that 60 AU the rotational evolution of young stars.

astro-ph↗

arXiv2001

An Adaptive Optics Survey for Companions to Stars with Extra-Solar Planets

We have undertaken an adaptive optics (AO) imaging survey of extrasolar planetary systems and stars showing interesting radial velocity trends from high precision radial velocity searches. AO increases the resolution and dynamic range of an image, substantially improving the detectability of faint close companions. This survey is sensitive to objects less luminous than the bottom of the main sequence at separations as close as 1 arcsec. We have detected stellar companions to the planet bearing stars HD 114762 and Tau Boo. We have also detected a companion to the non-planet bearing star 16 Cyg A.

astro-ph↗

arXiv1998

Discovery of seven T Tauri stars and a brown dwarf candidate in the nearby TW Hydrae Association

We report the discovery of five T Tauri star systems, two of which are resolved binaries, in the vicinity of the nearest known region of recent star formation, the TW Hydrae Association. The newly discovered systems display the same signatures of youth (namely high X-ray flux, large Li abundance and strong chromospheric activity) and the same proper motion as the original five members. These similarities firmly establish the group as a bona fide T Tauri association, unique in its proximity to Earth and its complete isolation from any known molecular clouds. At an age of ~10 Myr and a distance of ~50 pc, the association members are excellent candidates for future studies of circumstellar disk dissipation and the formation of brown dwarfs and planets. Indeed, as an example, our speckle imaging revealed a faint, very likely companion 2" north of CoD-33 7795 (TWA 5). Its color and brightness suggest a spectral type ~M8.5 which, at an age of ~10^7 years, implies a mass ~20 M(Jupiter).

astro-ph↗

arXiv1998

The Multiplicity of the Hyades and its Implications for Binary Star Formation and Evolution

A 2.2 micron speckle imaging survey of 167 bright (K $< 8.5$ mag) Hyades members reveals a total of 33 binaries with separations spanning 0."044 to 1."34 and magnitude differences as large as 5.5 mag. Of these binaries, 13 are new detections. Combining the results of this survey with previous radial velocity, optical speckle, and direct imaging Hyades surveys, the detected multiplicity of the sample is: 98 singles, 59 binaries, and 10 triples. A statistical analysis of this sample investigates a variety of multiple star formation and evolution theories. Accounting for the inability to detect high flux ratio binaries results in an implied companion star fraction (csf) of 0.30 +/- 0.06 in this separation range 0."1 to 1."07 (5 to 50 AU). The Hyades csf is intermediate between the values derived from observations of T Tauri stars (T Tauri csf=0.40 +/- 0.08) and solar neighborhood G-dwarfs (G-dwarf csf=0.14 +/- 0.03). This result allows for an evolution of the csf from an initially high value for the pre-main sequence to that found for main sequence stars. Within the Hyades, the csf is independent of the radial distance from the cluster center and the primary star mass. The distribution of mass ratios is best fit by a power law q^(-1.3 +/- 0.3) and shows no dependence on the primary mass, binary separation, or the radial distance from the cluster center. Overall, the Hyades data are consistent with scale-free fragmentation, but inconsistent with capture in small clusters and disk-assisted capture in small clusters. Without testable predictions, scale-dependent fragmentation and disk fragmentation cannot be assessed with the Hyades data.

astro-ph↗