arXiv subjects

H. Bouy

Publications and source records attributed to H. Bouy.

At least 109 records · Page 6Linked to original sources

arXiv2012

Searching for planetary-mass T-dwarfs in the core of Serpens

We searched for isolated planetary-mass T-dwarfs in the 3Myr old Serpens Core cluster. We performed a deep imaging survey of the central part of this cluster using the WIRCam camera at the CFHT. Observations were performed through the narrow-band CH4_off and CH4_on filters, to identify young T-dwarfs from their 1.6micr methane absorption bands, and the broad-band JHK filters, to better characterize the selected candidates. We complemented our WIRCam photometry with optical imaging data from MegaCam at CFHT and Suprime-Cam at the Subaru telescope and mid-IR flux measurements from the Spitzer c2d Legacy Survey. We report four faint T-dwarf candidates in the direction of the Serpens Core with CH4_on-CH4_off above 0.2 mag, estimated visual extinction in the range 1-9 mag and spectral type in the range T1-T5 based on their dereddened CH4_on-CH4_off colors. Comparisons with T-dwarf spectral models and optical to mid-IR color-color and color-magnitude diagrams, indicate that two of our candidates (ID1 and 2) are background contaminants (most likely heavily reddened low-redshift quasars). The properties of the other two candidates (ID3 and 4) are consistent with them being young members of the Serpens Core cluster, although our analysis can not be considered conclusive. In particular, ID3 may also be a foreground T-dwarf. It is detected by the Spitzer c2d survey but only flux upper limits are available above 5.8 microns and, hence, we can not assess the presence of a possible disk around this object. However, it presents some similarities with other young T-dwarf candidates (SOri70 in the Sigma Ori cluster and CFHTJ0344+3206 in the direction of IC348). If ID3 and 4 belong to Serpens, they would have a mass of a few Jupiter masses and would be amongst the youngest, lowest mass objects detected in a star-forming region so far.

astro-ph.SR↗

arXiv2012

A search for pre-substellar cores and proto-brown dwarf candidates in Taurus: multiwavelength analysis in the B213-L1495 clouds

In an attempt to study whether the formation of brown dwarfs (BDs) takes place as a scaled-down version of low-mass stars, we conducted IRAM30m/MAMBO-II observations at 1.2 mm in a sample of 12 proto-BD candidates selected from Spitzer/IRAC data in the B213-L1495 clouds in Taurus. Subsequent observations with the CSO at 350 micron, VLA at 3.6 and 6 cm, and IRAM30m/EMIR in the 12CO(1-0), 13CO(1-0), and N2H+(1-0) transitions were carried out toward the two most promising Spitzer/IRAC source(s), J042118 and J041757. J042118 is associated with a compact (<10 arcsec or <1400 AU) and faint source at 350 micron, while J041757 is associated with a partially resolved (~16 arcsec or ~2000 AU) and stronger source emitting at centimetre wavelengths with a flat spectral index. The corresponding masses of the dust condensations are ~1 and ~5 Mjup for J042118 and J041757, respectively. In addition, about 40 arcsec to the northeast of J041757 we detect a strong and extended submillimetre source, J041757-NE, which is not associated with NIR/FIR emission down to our detection limits, but is clearly detected in 13CO and N2H+ at ~7 km/s, and for which we estimated a total mass of ~100 Mjup, close to the mass required to be gravitationally bound. In summary, our observational strategy has allowed us to find in B213-L1495 two proto-BD candidates and one pre-substellar core candidate, whose properties seem to be consistent with a scaled-down version of low-mass stars.

astro-ph.GA↗

arXiv2012

Multiplicity in transiting planet host stars. A Lucky Imaging study of Kepler candidates

In the exoplanetary era, the Kepler spacecraft is causing a revolution by discovering thousands of new planet candidates. However, a follow up program is needed in order to reject false candidates and to fully characterize the bona-fide exoplanets. Our main aims are: 1./ Detect and analyze close companions inside the typical Kepler PSF to study if they are the responsible of the dim in the Kepler light curves, 2./ Study the change in the stellar and planetary parameters due to the presence of an unresolved object, 3./ Help to validate those Kepler Objects of Interest that do not present any object inside the Kepler PSF and 4./ Study the multiplicity rate in planet host candidates. Such a large sample of observed planet host candidates allows us to do statistics about the presence of close (visual or bounded) companions to the harboring star. We present here Lucky Imaging observations for a total amount of 98 Kepler Objects of Interest. This technique is based on the acquisition of thousands of very short exposure time images. Then, a selection and combination of a small amount of the best quality frames provides a high resolution image with objects having a 0.1 arcsec PSF. We applied this technique to carry out observations in the Sloan i and Sloan z filters of our Kepler candidates. We find blended objects inside the Kepler PSF for a significant percentage of KOIs. On one hand, only 58.2% of the hosts do not present any object within 6 arcsec. On the other hand, we have found 19 companions closer than 3 arcsec in 17 KOIs. According to their magnitudes and i-z color, 8 of them could be physically bounded to the host star.

astro-ph.EP↗

arXiv2012

Intermediate Resolution Near-Infrared Spectroscopy of 36 late-M Dwarfs

We present observations of 36 late-M dwarfs obtained with the KeckII/NIRSPEC in the J-band at a resolution of \sim20,000. We have measured projected rotational velocities, absolute radial velocities, and pseudo-equivalent widths of atomic lines. 12 of our targets did not have previous measurements in the literature. For the other 24 targets, we confirm previously reported measurements. We find that 13 stars from our sample have vsini below our measurement threshold (12 km/s) whereas four of our targets are fast rotators (vsini > 30 km/s). As fast rotation causes spectral features to be washed out, stars with low projected rotational velocities are sought for radial velocity surveys. At our intermediate spectral resolution we have confirmed the identification of neutral atomic lines reported in Mclean et al. 2007. We also calculated pseudo-equivalent widths (p-EW) of 12 atomic lines. Our results confirm that the p-EW of K I lines are strongly dependent on spectral types. We observe that the p-EW of Fe I and Mn I lines remain fairly constant with later spectral type. We suggest that those lines are particularly suitable for deriving metallicities for late-M dwarfs.

astro-ph.SR↗

arXiv2012

Spectroscopy of new brown dwarf members of rho Ophiuchi and an updated initial mass function

To investigate the universality hypothesis of the initial mass function in the substellar regime, the population of the rho Ophiuchi molecular cloud is analysed by including a new sample of low-mass spectroscopically confirmed members. To that end, we have conducted a large spectroscopic follow-up of young substellar candidates uncovered in our previous photometric survey. The spectral types and extinction were derived for a newly found population of substellar objects, and its masses estimated by comparison to evolutionary models. A thoroughly literature search was conducted to provide an up-to-date census of the cluster, which was then used to derive the luminosity and mass functions, as well as the ratio of brown dwarfs to stars in the cluster. These results were then compared to other young clusters. It is shown that the study of the substellar population of the rho Ophiuchi molecular cloud is hampered only by the high extinction in the cluster ruling out an apparent paucity of brown dwarfs. The discovery of 16 new members of rho Ophiuchi, 13 of them in the substellar regime, reveals the low-mass end of its population and shows the success of our photometric candidate selection with the WIRCam survey. The study of the brown dwarf population of the cluster reveals a high disk fraction of 76 (+5-8)%. Taking the characteristic peak mass of the derived mass function and the ratio of brown dwarfs to stars into account, we conclude that the mass function of rho Ophiuchi is similar to other nearby young clusters.

astro-ph.GA↗

arXiv2011

Spectroscopy of Very Low Mass Stars and Brown Dwarfs in the Lambda Orionis Star Forming Region. I. Enlarging the census down to the planetary mass domain in Collinder 69

Whilst there is a generally accepted evolutionary scheme for the formation of low-mass stars, the analogous processes when moving down in mass to the brown dwarfs regime are not yet well understood. In this first paper we try to build the most complete and unbiased spectroscopically confirmed census of the population of Collinder 69, the central cluster of the Lambda Orionis star forming region, as a first step in addressing the question of how brown dwarfs and planetary mass objects form. We have studied age dependent features in optical and near-infrared spectra of candidate members to the cluster (such as alkali lines and accretion associated indicators). In addition, we have complemented that study with the analysis of other youth indicators like X-ray emission or mid-infrared excess. We have confirmed the membership to Collinder 69 of \sim90 photometric candidate members. As a byproduct we have determined a temperature scale for young M, very low-mass stars and brown dwarfs. We have assembled one of the most complete Initial Mass Functions from 0.016 to 20 M\odot. And, finally, we have studied the implications of the spatial distribution of the confirmed members on the proposed mechanisms of brown dwarfs formation.

astro-ph.SR↗

arXiv2011

Young Stellar Objects in NGC 6823

NGC 6823 is a young open cluster that lies at a distance of ~2 kpc in the Vulpecula OB1 association. Previous studies using CCD photometry and spectroscopy have identified a Trapezium system of bright O- and B-type stars at its center. We present optical, near-infrared and Spitzer photometric observations of the cluster. Our survey reaches down to I~22 mag and Ks~18 mag. There is significant differential reddening within the cluster. We find a bimodal distribution for Av, with a peak at ~3 mag and a broader peak at ~10 mag. We find a ~20% fraction of Class I/Class II young stellar objects (YSOs) in the cluster, while a large 80% fraction of the sources have a Class III classification. We have made use of the IPHAS survey in order to probe the strength in Halpha emission for this large population of Class III sources. Nearly all of the Class III objects have photospheric (r'-Halpha) colors, implying an absence of Halpha in emission. This large population of Class III sources is thus likely the extincted field star population rather than the diskless YSOs in the cluster. There is a higher concentration of the Class I/II systems in the eastern region of the cluster and close to the central Trapezium. The western part of the cluster mostly contains Class III/field stars and seems devoid of disk sources. We find evidence of a pre-main sequence population in NGC 6823, in addition to an upper main-sequence population. The pre-main sequence population mainly consists of young disk sources with ages between ~1-5 Myr, and at lower masses of ~0.1-0.4 Msun. There may be a possible mass dependent age spread in the cluster, with the older stars being more massive than the younger ones. The presence of young disk sources in NGC 6823 indicates similar star formation properties in the outer regions of the Galaxy as observed for young clusters in the solar neighborhood.

astro-ph.SR↗

arXiv2010

Resolving the L/T transition binary SDSS J2052-1609 AB

Binaries provide empirical key constraints for star formation theories, like the overall binary fraction, mass ratio distribution and the separation distribution. They play a crucial role to calibrate the output of theoretical models, like absolute magnitudes, colors and effective temperature depending on mass, metallicity and age. We present first results of our on-going high-resolution imaging survey of late type brown dwarfs. The survey aims at resolving tight brown dwarf binary systems to better constrain the T dwarf binary fraction. We intent to follow-up the individual binaries to determine orbital parameters. Using NACO at the VLT we performed AO-assisted near-infrared observations of SDSS J2052-1609. High-spatial resolution images of the T1 dwarf were obtained in H and Ks filters. We resolved SDSS J2052-1609 into a binary system with a separation of 0.101" \pm 0.001". Archival data from HST/NICMOS taken one year previous to our observations proves the components to be co-moving. Using the flux ratio between the components we infer J, H and Ks magnitudes for the resolved system. From the near-IR colors we estimate spectral types of T1 +1 -4 and T2.5 \pm 1 for component A and B, respectively. A first estimate of the total system mass yields Mtot > 78 Mjup, assuming a circular orbit.

astro-ph.SR↗

arXiv2010

The search for planetary mass companions to field brown dwarfs with HST/NICMOS

We present the results of a high-resolution spectral differential imaging survey of 12 nearby, relatively young field L dwarfs (<1 Gyr) carried out with HST/NICMOS to search for planetary mass companions at small physical separations from their host. The survey resolved two brown dwarf binaries: the L dwarf system Kelu-1AB and the newly discovered L/T transition system 2MASS J031059+164815AB. For both systems common proper motion has already been confirmed in follow-up observations which have been published elsewhere. The derived separations of the binaries are smaller than 6 AU and consistent with previous brown dwarf binary statistics. Their mass ratios of q > 0.8 confirm the preference for equal mass systems similar to a large number of other surveys. Furthermore, we found tentative evidence for a companion to the L4 dwarf 2MASS W033703-175807, straddling the brown dwarf/planetary mass boundary and revealing an uncommonly low mass ratio system (q ~ 0.2) compared to the vast majority of previously found brown dwarf binaries. With a derived minimum mass of 10 - 15 Mjup, a planetary nature of the secondary cannot be ruled out yet. However, it seems more likely to be a very low mass brown dwarf secondary at the border of the spectral T/Y transition regime, primarily due to its similarities to recently found very cool T dwarfs. This would make it one of the closest resolved brown dwarf binaries (0.087" $/pm$ 0.015", corresponding to 2.52 $\pm$ 0.44 AU at a distance of 29 pc) with the coolest (Teff ~ 600-630 K) and least massive companion to any L or T dwarf.

astro-ph.SR↗

arXiv2010

Multi-wavelength study of the disk around the very low-mass star Par-Lup3-4

Par-Lup3-4 is a very low-mass star (spectral type M5) in the Lupus III star-forming region. The object is underluminous by ~4 mag when compared to objects of similar mass in the same association. To better understand the origin of its underluminosity, we have analyzed high angular resolution near-IR imaging data and mid-IR spectroscopy. We have also compared the SED of the target (from the optical to the sub-millimeter regime) to a grid of radiative transfer models of circumstellar disks. The diffraction-limited infrared observations do not show obvious extended emission, allowing us to put an upper limit to the disk outer radius of ~20AU. The lack of extended emission, together with the non detection of a strong 9.8 microns silicate in absorption indicates that Par-Lup3-4 is probably in a Class II (rather than Class I) evolutionary stage. The SED of Par-Lup3-4 resembles that of objects with edge-on disks seen in scattered light, that is, a double peaked-SED and a dip at ~10 microns. We can fit the whole SED with a single disk model with an inclination of 81+/-6 degrees which provides a natural explanation for the under-luminosity of the target. Our analysis allows to put constraints on the disk inner radius, Rin < 0.05 AU, which is very close to the dust sublimation radius, and the maximum size of the dust grains, a_max > 10 microns, which indicates that dust processing has already taken place in Par-Lup3-4.

astro-ph.SR↗

arXiv2010

Adaptive optics observations of the T10 ultracool dwarf UGPSJ072227.51-054031.2

With a spectral type of T10, UGPS J072227.51-054031.2 is one of the coolest objects known to date in the solar neighborhood. Multiple systems are relatively common among early and mid-T dwarfs. We search for faint and close companions around UGPSJ072227.51-054031.2. We have obtained high spatial resolution images in the H and Ks bands using adaptive optics at the Very Large Telescope. With a Strehl ratio in the range 10-15%, the final images allow us to rule out the presence of a companion brighter than H<19.4mag at separation larger than 50mas, and H<21.4mag at separation larger than 0.1".

astro-ph.SR↗

arXiv2010

Spectroscopic characterization of 78 DENIS ultracool dwarf candidates in the solar neighborhood and the Upper Sco OB association

Aims: Low-resolution optical spectroscopic observations for 78 very low-mass star and brown dwarf candidates that have been photometrically selected using the DENIS survey point source catalogue. Methods: Spectral types are derived for them using measurements of the PC3 index. They range from M6 to L4. H_alpha emission and NaI subordinate doublet (818.3 nm and 819.9 nm) equivalent widths are measured in the spectra. Spectroscopic indices of TiO, VO, CrH and FeH molecular features are also reported. Results: A rule-of-thumb criterion to select young very low-mass objects using the NaI doublet equivalent width is given. It is used to confirm seven new members of the Upper Sco OB association and two new members of the R Cr-A star-forming region. Four of our field objects are also classified as very young, but are not members of any known nearby young association. The frequency of lower-gravity young objects in our field ultracool sample is 8.5%. Our results provide the first spectroscopic classification for 38 ultracool dwarfs in the solar vicinity with spectrophotometric distances in the range 17 pc to 65 pc (3 of them are new L dwarfs within 20 pc).

astro-ph.SR↗

arXiv2010

2MASS J03105986+1648155AB - A new binary at the L/T transition

The transition from the L to the T spectral type of brown dwarfs is marked by a very rapid transition phase, remarkable brightening in the J-band and a higher binary frequency. Despite being an active area of inquiry, this transition regime still remains one of the most poorly understood phases of brown dwarf evolution. We resolved the L dwarf 2MASS J03105986+1648155 for the first time into two almost equally bright components straddling the L/T transition. Since such a co-eval system with common age and composition provides crucial information of this special transition phase, we monitored the system over 3 years to derive first orbital parameters and dynamical mass estimates, as well as a spectral type determination. We obtained resolved high angular resolution, near-IR images with HST and the adaptive optics instrument NACO at the VLT including the laser guide star system PARSEC. Based on two epochs of astrometric data we derive a minimum semi-major axis of 5.2 +- 0.8 AU. The assumption of a face-on circular orbit yields an orbital period of 72 +- 4 years and a total system mass of 30-60 Mjup. This places the masses of the individual components of the system at the lower end of the mass regime of brown dwarfs. The achieved photometry allowed a first spectral type determination of L9 +- 1 for each component. In addition, this seems to be only the fifth resolved L/T transition binary with a flux reversal. While ultimate explanations for this effect are still owing, the 2MASS J03105986+1648155 system adds an important benchmark object for improving our understanding of this remarkable evolutionary phase of brown dwarfs. Additionally, the observational results of 2MASS J03105986+1648155 AB derived with the new PARSEC AO system at the VLT show the importance of this technical capability. The updated AO system allows us to significantly extend the sample of brown dwarfs observable with high-resolution from the ground and hence to reveal more of their physical properties.

astro-ph.SR↗

arXiv2010

The low-mass population of the Rho Ophiuchi molecular cloud

Star formation theories are currently divergent regarding the fundamental physical processes that dominate the substellar regime. Observations of nearby young open clusters allow the brown dwarf (BD) population to be characterised down to the planetary mass regime, which ultimately must be accommodated by a successful theory. We hope to uncover the low-mass population of the Rho Ophiuchi molecular cloud and investigate the properties of the newly found brown dwarfs. We use near-IR deep images (reaching completeness limits of approximately 20.5 mag in J, and 18.9 mag in H and Ks) taken with the Wide Field IR Camera (WIRCam) at the Canada France Hawaii Telescope (CFHT) to identify candidate members of Rho Oph in the substellar regime. A spectroscopic follow-up of a small sample of the candidates allows us to assess their spectral type, and subsequently their temperature and membership. We select 110 candidate members of the Rho Ophiuchi molecular cloud, from which 80 have not previously been associated with the cloud. We observed a small sample of these and spectroscopically confirm six new brown dwarfs with spectral types ranging from M6.5 to M8.25.

astro-ph.GA↗

arXiv2009

Panchromatic observations and modeling of the HV Tau C edge-on disk

We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8 and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images reveal an unusually slow orbital motion within the tight HV Tau AB pair that suggests a highly eccentric orbit and/or a large deprojected physical separation. Scattered light images of the HV Tau C edge-on protoplanetary disk suggest that the anisotropy of the dust scattering phase function is almost independent of wavelength from 0.8 to 5 micron, whereas the dust opacity decreases significantly over the same range. The images further reveal a marked lateral asymmetry in the disk that does not vary over a timescale of 2 years. We further detect a radial velocity gradient in the disk in our 12CO map that lies along the same position angle as the elongation of the continuum emission, which is consistent with Keplerian rotation around an 0.5-1 Msun central star, suggesting that it could be the most massive component in the triple system. We use a powerful radiative transfer model to compute synthetic disk observations and use a Bayesian inference method to extract constraints on the disk properties. Each individual image, as well as the spectral energy distribution, of HV Tau C can be well reproduced by our models with fully mixed dust provided grain growth has already produced larger-than-interstellar dust grains. However, no single model can satisfactorily simultaneously account for all observations. We suggest that future attempts to model this source include more complex dust properties and possibly vertical stratification. (Abridged)

astro-ph.SR↗

arXiv2009

Optical linear polarization in ultra cool dwarfs: A tool to probe dust in the ultra cool dwarf atmospheres

Aims.Recent studies have detected linear polarization in L dwarfs in the optical I band. Theoretical models have been developed to explain this polarization. These models predict higher polarization at shorter wavelengths. We discuss the polarization in the R and I band of 4 ultra cool dwarfs. Methods.We report linear polarization measurements of 4 ultra cool dwarfs in the R and I bands using the Intermediate dispersion Spectrograph and Imaging System (ISIS) mounted on the 4.2m William Herschel Telescope (WHT). Results.As predicted by theoretical models, we find a higher degree of polarization in the R band when compared to polarization in the I band for 3/4 of these ultra cool dwarfs. This suggests that dust scattering asymmetry is caused by oblateness >.We also show how these measurements fit the theoretical models. A case for variability of linear polarization is found, which suggests the presence of randomly distributed dust clouds. We also discuss one case for the presence of a cold debris disk.

astro-ph.SR↗

arXiv2009

Young T-Dwarf Candidates in IC 348

The determination of the lower-end of the initial mass function (IMF) provides strong constraints on star formation theories. We report here on a search for isolated planetary-mass objects in the 3 Myr-old star-forming region IC 348. Deep, narrowband CH4off and CH4on images were obtained with CFHT/WIRCam over 0.11 sq.deg. in the central part of IC 348 to identify young T-dwarfs from their 1.6 um methane absorption bands. We report three faint T-dwarf candidates with CH4on-CH4off colours > 0.4 mag. Extinction was estimated for each candidate and lies in the range Av ~ 5-12 mag. Comparisons with T-dwarf spectral models, and colour/colour and colour/magnitude diagrams, reject two of the three candidates because of their extreme z' - J blueness. The one remaining object is not thought to be a foreground field dwarf because of a number density argument and also its strong extinction Av - 12 mag, or thought to be a background field T-dwarf which would be expected to be much fainter. Models and diagrams give this object a preliminary T6 spectral type. With a few Jupiter masses, the young T-dwarf candidate reported here is potentially amongst the youngest, lowest mass objects detected in a star-forming region so far. Its frequency is consistent with the extrapolation of current lognormal IMF estimates down to the planetary mass domain.

astro-ph.SR↗

arXiv2009

A deep look into the core of young clusters. II. lambda-Orionis

Over the past years, the lambda-Orionis cluster has been a prime location for the study of young very low mass stars, substellar and isolated planetary mass objects and the determination of the initial mass function and other properties of low mass cluster members. In the continuity of our previous studies of young associations cores, we search for ultracool members and new multiple systems within the central 5.3' (~0.6pc) of the cluster. We obtained deep seeing limited J, Ks-band images of the 5.3' central part of the cluster with NTT/SofI and H-band images with CAHA/Omega2000. These images were complemented by multi-conjugate adaptive optics (MCAO) H and Ks images of the 1.5' central region of the lambda-Orionis cluster obtained with the prototype MCAO facility MAD at the VLT. The direct vicinity of the massive lambda-Ori O8III-star was probed using NACO/SDI at the VLT. Finally, we also retrieved Spitzer IRAC images of the same area and used archival Subaru Suprime-Cam and CFHT CFHT12K i-band images. We report the detection of 9 new member candidates selected from optical and near-IR color-color and color-magnitude diagrams and 7 previously known members. The high spatial resolution images resolve 3 new visual multiple systems. Two of them are most likely not members of the association. The third one is made of a brown dwarf candidate companion to the F8V star HD36861C. The simultaneous differential images allow us to rule out the presence of visual companions more massive than M>0.07Msun in the range 1-2.5", and M>0.25Msun in the range 0.5-2.5"

astro-ph.SR↗