arXiv subjects

Lison Malo

Publications and source records attributed to Lison Malo.

At least 55 records · Page 3Linked to original sources

arXiv2016

BANYAN. VIII. New Low-Mass Stars and Brown Dwarfs with Candidate Circumstellar Disks

We present the results of a search for new circumstellar disks around low-mass stars and brown dwarfs with spectral types >K5 that are confirmed or candidate members of nearby young moving groups. Our search input sample was drawn from the BANYAN surveys of Malo et al. and Gagné et al. Two-Micron All-Sky Survey and Wide-field Infrared Survey Explorer data were used to detect near- to mid-infrared excesses that would reveal the presence of circumstellar disks. A total of 13 targets with convincing excesses were identified: four are new and nine were already known in the literature. The new candidates are 2MASS J05010082$-$4337102 (M4.5), J08561384$-$1342242 (M8$\,γ$), J12474428$-$3816464 (M9$\,γ$) and J02265658$-$5327032 (L0$\,δ$), and are candidate members of the TW Hya ($\sim10\pm 3\,$Myr), Columba ($\sim 42^{+6}_{-4}\,$Myr) and Tucana-Horologium ($\sim 45\pm 4\,$Myr) associations, with masses of $120$ and $13-18\,M_{\mathrm{Jup}}$. The M8$-$L0 objects in Columba and Tucana-Horologium are potentially among the first substellar disk systems aged $\sim 40\,$Myr. Estimates of the new candidates' mean disk temperatures and fractional luminosities are in the ranges $\sim 135-520\,$K and $0.021-0.15$, respectively. New optical spectroscopy of J0501$-$4337 reveals strong H$α$ emission, possibly indicating ongoing accretion, provides a detection of lithium absorption and a radial velocity measurement that is consistent with a membership to Columba. We also present a near-infrared spectrum of J0226$-$5327 that reveals Paschen $β$ emission and shows signs of low surface gravity, consistent with accretion from a disk and a young age.

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arXiv2016

GRACES observations of young [alpha/Fe]-rich stars

We measure chemical abundance ratios and radial velocities in four massive (i.e., young) [alpha/Fe]-rich red giant stars using high-resolution high-S/N spectra from ESPaDOnS fed by Gemini-GRACES. Our differential analysis ensures that our chemical abundances are on the same scale as the Alves-Brito et al. (2010) study of bulge, thin and thick disk red giants. We confirm that the program stars have enhanced [alpha/Fe] ratios and are slightly metal poor. Aside from lithium enrichment in one object, the program stars exhibit no chemical abundance anomalies when compared to giant stars of similar metallicity throughout the Galaxy. This includes the elements Li, O, Si, Ca, Ti, Cr, Ni, Cu, Ba, La, and Eu. Therefore, there are no obvious chemical signatures that can help to reveal the origin of these unusual stars. While our new observations show that only one star (not the Li-rich object) exhibits a radial velocity variation, simulations indicate that we cannot exclude the possibility that all four could be binaries. In addition, we find that two (possibly three) stars show evidence for an infrared excess, indicative of a debris disk. This is consistent with these young [alpha/Fe]-rich stars being evolved blue stragglers, suggesting their apparent young age is a consequence of a merger or mass transfer. We would expect a binary fraction of ~50% or greater for the entire sample of these stars, but the signs of the circumbinary disk may have been lost since these features can have short timescales. Radial velocity monitoring is needed to confirm the blue straggler origin.

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arXiv2015

BANYAN. VII. A New Population of Young Substellar Candidate Members of Nearby Moving Groups from the BASS Survey

[Abbreviated] We present the results of a near-infrared (NIR) spectroscopic follow-up survey of 182 M4-L7 low-mass stars and brown dwarfs (BDs) from the BANYAN All-Sky Survey (BASS) for candidate members of nearby, young moving groups (YMGs). We confirm signs of low-gravity for 42 new BD discoveries with estimated masses between 8-75 $M_{Jup}$ and identify previously unrecognized signs of low gravity for 24 known BDs. This allows us to refine the fraction of low-gravity dwarfs in the high-probability BASS sample to $\sim$82%. We use this unique sample of 66 young BDs, supplemented with 22 young BDs from the literature, to construct new empirical NIR absolute magnitude and color sequences for low-gravity BDs. We obtain a spectroscopic confirmation of low-gravity for 2MASS J14252798-3650229, which is a new $\sim$27 $M_{Jup}$, L4 $γ$ bona fide member of AB Doradus. We identify a total of 19 new low-gravity candidate members of YMGs with estimated masses below 13 $M_{Jup}$, seven of which have kinematically estimated distances within 40 pc. These objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments. We find 16 strong candidate members of the Tucana-Horologium association with estimated masses between 12.5-14 $M_{Jup}$, a regime where our study was particularly sensitive. This would indicate that for this association there is at least one isolated object in this mass range for every $17.5_{-5.0}^{+6.6}$ main-sequence stellar member, a number significantly higher than expected based on standard log-normal initial mass function, however in the absence of radial velocity and parallax measurements for all of them, it is likely that this over-density is caused by a number of young interlopers from other moving groups. We identify 12 new L0-L5 field BDs, seven of which display peculiar properties.

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arXiv2015

The BANYAN All-Sky Survey for Brown Dwarf Members of Young Moving Groups

We describe in this work the BASS survey for brown dwarfs in young moving groups of the solar neighborhood, and summarize the results that it generated. These include the discovery of the 2MASS J01033563-5515561 (AB)b and 2MASS J02192210-3925225 B young companions near the deuterium-burning limit as well as 44 new low-mass stars and 69 new brown dwarfs with a spectroscopically confirmed low gravity. Among those, ~20 have estimated masses within the planetary regime, one is a new L4 $γ$ bona fide member of AB Doradus, three are TW Hydrae candidates with later spectral types (L1-L4) than all of its previously known members and six are among the first contenders to low-gravity $\geq$ L5 $β$/$γ$ brown dwarfs, reminiscent of WISEP J004701.06+680352.1, PSO J318.5338-22.8603 and VHS J125601.92-125723.9 b. Finally, we describe a future version of this survey, BASS-Ultracool, that will specifically target $\geq$ L5 candidate members of young moving groups. First experimentations in designing the survey have already led to the discovery of a new T dwarf member of AB Doradus, as well as the serendipitous discoveries of an L9 subdwarf and an L5 + T5 brown dwarf binary.

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arXiv2015

BANYAN. VI. Discovery of a companion at the brown dwarf/planet-mass limit to a Tucana-Horologium M dwarf

We report the discovery of a substellar companion to 2MASS J02192210-3925225, a young M6 $γ$ candidate member of the Tucana-Horologium association (30 - 40 Myr). This L4 $γ$ companion has been discovered with seeing-limited direct imaging observations; at a 4" separation (160AU) and a modest contrast ratio, it joins the very short list of young low-mass companions amenable to study without the aid of adaptive optics, enabling its characterization with a much wider suite of instruments than is possible for companions uncovered by high-contrast imaging surveys. With a model-dependent mass of 12-15MJup, it straddles the boundary between the planet and brown dwarf mass regimes. We present near-infrared spectroscopy of this companion and compare it to various similar objects uncovered in the last few years. The J0219-3925 system falls in a sparsely populated part of the host mass versus mass ratio diagram for binaries; the dearth of known similar companions may be due to observational biases in previous low-mass companion searches.

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arXiv2015

Discovery And Characterization of Wide Binary Systems With a Very Low Mass Component

We report the discovery of 14 low-mass binary systems containing mid-M to mid-L dwarf companions with separations larger than 250 AU. We also report the independent discovery of 9 other systems with similar characteristics that were recently discovered in other studies. We have identified these systems by searching for common proper motion sources in the vicinity of known high proper motion stars, based on a cross-correlation of wide area near-infrared surveys (2MASS, SDSS, and SIMP). An astrometric follow-up, for common proper motion confirmation, was made with SIMON and/or CPAPIR at the OMM 1.6 m and CTIO 1.5 m telescopes for all the candidates identified. A spectroscopic follow-up was also made with GMOS or GNIRS at Gemini to determine the spectral types of 11 of our newly identified companions and 10 of our primaries. Statistical arguments are provided to show that all of the systems we report here are very likely to be physical binaries. One of the new systems reported features a brown dwarf companion: LSPM J1259+1001 (M5) has an L4.5 (2M1259+1001) companion at about 340 AU. This brown dwarf was previously unknown. Seven other systems have a companion of spectral type L0-L1 at a separation in the 250-7500 AU range. Our sample includes 14 systems with a mass ratio below 0.3.

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arXiv2014

BANYAN. V. A Systematic All-Sky Survey for New Very Late-Type Low-Mass Stars and Brown Dwarfs in Nearby Young Moving Groups

We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ~ 13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the 2MASS and ALLWISE catalogs outside of the galactic plane to build a sample of 98 970 potential $\geq$ M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15 mas yr$^{-1}$. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by $\geq$ M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs.

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arXiv2014

Results from BASS, the BANYAN All-Sky Survey

We present results from the BANYAN All-Sky Survey (BASS), a systematic all-sky survey for brown dwarf candidates in young moving groups. We describe a cross-match of the 2MASS and AllWISE catalogs that provides a list of 98 970 potential nearby dwarfs with spectral types later than M5 with measurements of proper motion at precisions typically better than 15 mas yr$^{-1}$, as well as the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II) which we use to build the BASS catalog from this 2MASS-AllWISE cross-match, consisting of more than 300 candidate members of young moving groups. We present the first results of a spectroscopic follow-up of those candidates, which allowed us to identify several new low-mass stars and brown dwarfs displaying signs of low gravity. We use the BASS catalog to show tentative evidence for mass segregation in AB Doradus and Argus, and reveal a new $\sim$ 13 M$_{Jup}$ co-moving companion to a young low-mass star in BASS. We obtain a moderate-resolution near-infrared spectrum for the companion, which reveals typical signs of youth and a spectral type L4 $γ$.

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arXiv2014

GRACES: Gemini remote access to CFHT ESPaDOnS Spectrograph through the longest astronomical fiber ever made (Experimental phase completed.)

The Gemini Remote Access to CFHT ESPaDONS Spectrograph has achieved first light of its experimental phase in May 2014. It successfully collected light from the Gemini North telescope and sent it through two 270 m optical fibers to the the ESPaDOnS spectrograph at CFHT to deliver high-resolution spectroscopy across the optical region. The fibers gave an average focal ratio degradation of 14% on sky, and a maximum transmittance of 85% at 800nm. GRACES achieved delivering spectra with a resolution power of R = 40,000 and R = 66,000 between 400 and 1,000 nm. It has a ~8% throughput and is sensitive to target fainter than 21st mag in 1 hour. The average acquisition time of a target is around 10 min. This project is a great example of a productive collaboration between two observatories on Maunakea that was successful due to the reciprocal involvement of the Gemini, CFHT, and NRC Herzberg teams, and all the staff involved closely or indirectly.

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arXiv2014

SIMP J2154-1055: A New Low-Gravity L4$β$ Brown Dwarf Candidate Member of the Argus Association

We present SIMP J21543454-1055308, a new L4$β$ brown dwarf identified in the Sondage Infrarouge de Mouvement Propre (SIMP) survey that displays signs of low gravity in its near-infrared spectrum. Using the Bayesian Analysis for Nearby Young AssociatioNs II (BANYAN II), we show that it is a candidate member of the Argus association, albeit with a 21% probability that it is a contaminant from the field. Measurements of radial velocity and parallax will be needed to verify its membership. If it is a member of Argus (age 30-50 Myr), then this object would have a planetary mass of 10 $\pm$ 0.5 $M_{\mathrm{Jup}}$.

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arXiv2014

Telluric-line subtraction in high-accuracy velocimetry: a PCA-based approach

Optical velocimetry has led to the detection of more than 500 planets to date and there is a strong effort to push m/s velocimetry to the near-infrared to access cooler and lighter stars. The presence of numerous telluric absorption lines in the nIR brings an important challenge. As the star's barycentric velocity varies through the year, the telluric absorption lines effectively varies in velocity relative to the star's spectrum by the same amount leading to important systematic RV offsets. We present a novel principal component analysis-based approach for telluric line subtraction and demonstrated its effectiveness with archival HARPS data for GJ436 and τ Ceti, over parts of the R-band that contain strong telluric absorption lines. The main results are: 1) a better RV accuracy with excluding only a few percentage of the domain, 2) better use of the entire spectrum to measure RV and 3) a higher telescope time efficency by using A0V telluric standard from telescope archive.

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arXiv2014

BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups - Isochronal Age determination using Magnetic evolutionary models

Based on high resolution optical spectra obtained with ESPaDOnS at CFHT, we determine fundamental parameters (\Teff, R, \Lbol, \logg\ and metallicity) for 59 candidate members of nearby young kinematic groups. The candidates were identified through the BANYAN Bayesian inference method of \citet{2013malo}, which takes into account the position, proper motion, magnitude, color, radial velocity and parallax (when available) to establish a membership probability. The derived parameters are compared to Dartmouth Magnetic evolutionary models and to field stars with the goal to constrain the age of our candidates. We find that, in general, low-mass stars in our sample are more luminous and have inflated radii compared to older stars, a trend expected for pre-main sequence stars. The Dartmouth Magnetic evolutionary models show a good fit to observations of field K and M stars assuming a magnetic field strength of a few kG, as typically observed for cool stars. Using the low-mass members of $β$Pictoris moving group, we have re-examined the age inconsistency problem between Lithium Depletion age and isochronal age (Hertzspring-Russell diagram). We find that the inclusion of the magnetic field in evolutionary models increase the isochronal age estimates for the K5V-M5V stars. Using these models and field strengths, we derive an average isochronal age between 15 and 28 Myr and we confirm a clear Lithium Depletion Boundary from which an age of 26$\pm$3~Myr is derived, consistent with previous age estimates based on this method.

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arXiv2014

Discovery of a wide planetary-mass companion to the young M3 star GU Psc

We present the discovery of a co-moving planetary-mass companion ~42" (~2000 AU) from a young M3 star, GU Psc, likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i - z color (> 3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5+-1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates Teff = 1000-1100 K and logg = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 MJup for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE.

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arXiv2014

The Coolest Isolated Brown Dwarf Candidate Member of TWA

We present two new late-type brown dwarf candidate members of the TW Hydrae association (TWA) : 2MASS J12074836-3900043 and 2MASS J12474428-3816464, which were found as part of the BANYAN all-sky survey (BASS) for brown dwarf members to nearby young associations. We obtained near-infrared (NIR) spectroscopy for both objects (NIR spectral types are respectively L1 and M9), as well as optical spectroscopy for J1207-3900 (optical spectral type is L0γ), and show that both display clear signs of low-gravity, and thus youth. We use the BANYAN II Bayesian inference tool to show that both objects are candidate members to TWA with a very low probability of being field contaminants, although the kinematics of J1247-3816 seem slightly at odds with that of other TWA members. J1207-3900 is currently the latest-type and the only isolated L-type candidate member of TWA. Measuring the distance and radial velocity of both objects is still required to claim them as bona fide members. Such late-type objects are predicted to have masses down to 11-15 MJup at the age of TWA, which makes them compelling targets to study atmospheric properties in a regime similar to that of currently known imaged extrasolar planets.

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arXiv2014

BANYAN. III. Radial velocity, Rotation and X-ray emission of low-mass star candidates in nearby young kinematic groups

Based on high-resolution spectra obtained with PHOENIX at Gemini-South, CRIRES at VLT-UT1, and ESPaDOnS at CFHT, we present new measurements of the radial and projected rotational velocities of 219 low-mass stars. The target likely membership was initially established using the Bayesian analysis tool recently presented in \citet{2013malo}, taking into account only the position, proper motion and photometry of the stars to assess their membership probability. In the present study, we include radial velocity as an additional input to our analysis, and in doing so we confirm the high membership probability for 130 candidates: 27 in $β$ Pictoris, 22 in Tucana-Horologium, 25 in Columba, 7 in Carina, 18 in Argus and 18 in AB Doradus and 13 with an ambiguous membership. Our analysis also confirms the membership of 57 stars proposed in the literature. A subsample of 16 candidates was observed at three or more epochs, allowing us to discover 6 new spectroscopic binaries. The fraction of binaries in our sample is 25%, consistent with values in the literature. Twenty percent of the stars in our sample show projected rotational velocities (\vsini) higher than 30 \kms\ and therefore are considered as fast rotators. A parallax and other youth indicators are still needed to fully confirm the 130 highly probable candidates identified here as new {\it bona fide} members. Finally, based on the X-ray emission of {\it bona fide} and highly probable group members, we show that for low-mass stars in the 12-120 Myr age range, the X-ray luminosity is an excellent indicator of youth and better than the more traditionally used R$_{\rm X}$ parameter, the ratio of X-ray to bolometric luminosity.

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arXiv2014

BANYAN. II. Very Low Mass and Substellar Candidate Members to Nearby, Young Kinematic Groups With Previously Known Signs of Youth

We present Bayesian Analysis for Nearby Young AssociatioNs II (BANYAN II), a modified Bayesian analysis for assessing the membership of later-than-M5 objects to any of several Nearby Young Associations (NYAs). In addition to using kinematic information (from sky position and proper motion), this analysis exploits 2MASS-WISE color-magnitude diagrams in which old and young objects follow distinct sequences. As an improvement over our earlier work, the spatial and kinematic distributions for each association are now modelled as ellipsoids whose axes need not be aligned with the Galactic coordinate axes, and we use prior probabilities matching the expected populations of the NYAs considered versus field stars. We present an extensive contamination analysis to characterize the performance of our new method. We find that Bayesian probabilities are generally representative of contamination rates, except when a parallax measurement is considered. In this case contamination rates become significantly smaller and hence Bayesian probabilities for NYA memberships are pessimistic. We apply this new algorithm to a sample of 158 objects from the literature that are either known to display spectroscopic signs of youth or have unusually red near-infrared colors for their spectral type. Based on our analysis, we identify 25 objects as new highly probable candidates to NYAs, including a new M7.5 bona fide member to Tucana-Horologium, making it the latest-type member. In addition, we reveal that a known L2γ dwarf is co-moving with a bright M5 dwarf, and we show for the first time that two of the currently known ultra red L dwarfs are strong candidates to the AB Doradus moving group. Several objects identified here as highly probable members to NYAs could be free-floating planetary-mass objects if their membership is confirmed.

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arXiv2014

The Solar Neighborhood. XXXIII. Parallax Results from the CTIOPI 0.9m Program: Trigonometric Parallaxes of Nearby Low-Mass Active and Young Systems

We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing RECONS photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log(Lx/Lbol) > -3.5) based on X-ray fluxes from the ROSAT All-Sky Survey, and many are significantly more luminous than main-sequence stars of comparable color. We present parallaxes and proper motions, Johnson-Kron-Cousins VRI photometry, and multiplicity observations from the CTIOPI program on the CTIO 0.9m telescope. To this we add low-resolution optical spectroscopy and line measurements from the CTIO 1.5m telescope, and interferometric binary measurements from the Hubble Space Telescope Fine Guidance Sensors. We also incorporate data from published sources: JHKs photometry from the 2MASS point source catalog; X-ray data from the ROSAT All-Sky Survey; and radial velocities from literature sources. Within the sample of 45 systems, we identify 21 candidate low-mass pre-main-sequence members of nearby associations, including members of beta Pictoris, TW Hydrae, Argus, AB Doradus, two ambiguous 30 Myr old systems, and one object that may be a member of the Ursa Major moving group. Of the 21 candidate young systems, 14 are newly identified as a result of this work, and six of those are within 25 parsecs of the Sun.

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arXiv2013

Bayesian analysis to identify very low-mass members of nearby young stellar kinematic groups

We describe our all-sky survey for >M4 candidate members to nearby, young associations from the 2MASS and WISE catalogs using bayesian inference. We report the first results, including 38 highly probable candidates showing spectroscopic signs of low-gravity (and thus youth). The latest of these objects would correspond to a 11 - 13 MJup object, around the limit of the planetary regime.

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