We present MIPS 24um and 70um photometry for 205 members of the Upper Scorpius OB Association. These data are combined with published MIPS photometry for 15 additional association members to assess the frequency of circumstellar disks around 5 Myr old stars with spectral types between B0 and M5. Twelve stars have a detectable 70um excess, each of which also has a detectable 24um excess. A total of 54 stars are identified with a 24um excess more than 32% above the stellar photosphere. The MIPS observations reveal 19 excess sources -- 8 A/F/G stars and 11 K/M stars -- that were not previously identified with an 8um or 16um excess. The lack of short-wavelength emission and the weak 24um excess suggests that these sources are debris systems or the remnants of optically thick primordial disks with inner holes. Despite the wide range of luminosities of the stars hosting apparent debris systems, the excess characteristics are consistent with all stars having dust at similar orbital radii after factoring in variations in the radiation blowout particle size with spectral type. The results for Upper Sco are compared to similar photometric surveys from the literature to re-evaluate the evolution of debris emission. After considering the completeness limits of published surveys and the effects of stellar evolution on the debris luminosity, we find that the magnitude of the 24um excess around F-type stars increases between ages of 5 and 17 Myr as found by previous studies, but at < 2.6 sigma confidence. For B7-A9 and G0-K5 stars, any variations in the observed 24um excess emission over this age range are significant at less than 2 sigma confidence.
This paper presents the results of a search for brown dwarfs in the Upper Scorpius Association using data from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey. Candidate young brown dwarfs were first chosen by their position in colour magnitude diagrams with further selection based on proper motions to ensure Upper Scorpius membership. Proper motions were derived by comparing UKIDSS and 2MASS data. Using that method we identify 19 new brown dwarfs in the southern part of the association. In addition there are up to 8 likely members with slightly higher dispersion velocity. …
Proper motion measurements of the cool and ultracool populations in the Upper Scorpius OB association are crucial to confirm membership and to identify possible run-away objects. We cross-match samples of photometrically selected and spectroscopically confirmed cool and ultracool (K5<SpT<M8.5) candidate members in the Upper Scorpius OB association using the literature and the USNO-B and the UCAC2 catalogues. 251 of these objects have a USNO-B and/or UCAC2 counterpart with proper motion measurements. A significant fraction (19 objects, 7.6+-1.8%) of spectroscopically confirmed young objects sho…
We analyze Spitzer IRS spectra of 110 B-, A-, F-, and G-type stars with optically thin infrared excess in the Scorpius-Centaurus (ScoCen) OB association. The age of these stars ranges from 11-17 Myr. We fit the infrared excesses observed in these sources by Spitzer IRS and Spitzer MIPS to simple dust models according to Mie theory. We find that nearly all the objects in our study can be fit by one or two belts of dust. Dust around lower mass stars appears to be closer in than around higher mass stars, particularly for the warm dust component in the two-belt systems, suggesting mass-dependent e…
Upper Scorpius is a subgroup of the nearest OB association, Scorpius--Centaurus. Its young age makes it an important association to study star and planet formation. We present parallaxes to 52 low mass stars in Upper Scorpius, 28 of which have full kinematics. We measure ages of the individual stars by combining our measured parallaxes with pre-main sequence evolutionary tracks. We find there is a significant difference in the ages of stars with and without circumstellar disks. The stars without disks have a mean age of 4.9+/-0.8 Myr and those with disks have an older mean age of 8.2+/-0.9 Myr…
Using new proper motion data from recently published catalogs, we revisit the membership of previously identified members of the Upper Scorpius association. We confirmed 750 of them as cluster members based on the convergent point method, compute their kinematic parallaxes and combined them with Gaia parallaxes to investigate the 3D structure and geometry of the association using a robust covariance method. We find a mean distance of $146\pm 3\pm 6$~pc and show that the morphology of the association defined by the brightest (and most massive) stars yields a prolate ellipsoid with dimensions of…
We report on a deep photometric survey covering an area of 1.17 deg$^2$ in the young Upper Scorpius stellar association using VIMOS $Iz$ and UKIDSS $ZJHK$ data taking several years apart. The search for the least massive population of Upper Scorpius ($\sim$5-10 Myr, 145 pc) is performed on the basis of various optical and infrared color-color and color-magnitude diagrams, including WISE photometry, in the magnitude interval $J$=14.5-19 mag (completeness), which corresponds to substellar masses from 0.028 through 0.004 M$_\odot$ at the age and distance of Upper Scorpius. We also present the pro…
We aim at identifying very low-mass isolated planetary-mass member candidates in the nearest OB association to the Sun, Upper Scorpius (145 pc; 5-10 Myr), to constrain the form and shape of the luminosity function and mass spectrum in this regime. We conducted a deep multi-band ($Y$=21.2, $J$=20.5, $Z$=22.0 mag) photometric survey of six square degrees in the central region of Upper Scorpius. We extend the current sequence of astrometric and spectroscopic members by about two magnitudes in $Y$ and one magnitude in $J$, reaching potentially T-type free-floating members in the association with p…
We present mid-infrared spectra between 5.2 and 38 microns for 26 disk-bearing members of the ~5 Myr old Upper Scorpius OB association obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope. We find clear evidence for changes in the spectral characteristics of dust emission between the early (B+A) and late-type (K+M) infrared excess stars. The early-type members exhibit featureless continuum excesses that become apparent redward of ~8 microns. In contrast, 10 and 20 micron silicate features are present in all but one of the late-type excess members of Upper Scorpius. The s…
We report the serendipitous discovery of several young mid-M stars found during a search for new members of the 30-40 Myr-old Octans Association. Only one of the stars may be considered a possible Octans(-Near) member. However, two stars have proper motions, kinematic distances, radial velocities, photometry and Li I 6708AA measurements consistent with membership in the 8-10 Myr-old TW Hydrae Association. Another may be an outlying member of TW Hydrae but has a velocity similar to that predicted by membership in Octans. We also identify two new lithium-rich members of the neighbouring Scorpius…
Moderate-resolution, near-infrared spectra between 0.8 and 5.2 microns were obtained for 12 late-type (K0-M3) disk-bearing members of the ~5 Myr old Upper Scorpius OB association using SpeX on the NASA Infrared Telescope Facility. For most sources, continuum excess emission first becomes apparent between ~2.2 and 4.5 microns and is consistent with that produced by single-temperature blackbodies having characteristic temperatures ranging from ~500 to 1300 K. The near-infrared spectra for 5 of 12 Upper Scorpius sources exhibit Pa-gamma, Pa-beta and Br-gamma emission, indicators of disk accretion…
Young stellar associations represent a key site for the study of star formation, but to accurately compare observations to models of stellar evolution, the age of an association must be determined. The Upper Scorpius region is the youngest section of the Scorpius-Centaurus OB association, which is the largest collection of nearby, young, low-mass stars. The true age of Upper Scorpius is not clear, and an observed mass-dependent age gradient in Upper Scorpius, as well as in other star-forming regions, complicates age measurements. The age gradient may indicate a genuine astrophysical feature or…
We present ALMA 880 micron continuum observations of 20 K and M-type stars in the Upper Scorpius OB association that are surrounded by protoplanetary disks. These data are used to measure the dust content in disks around low mass stars (0.1-1.6 Msun) at a stellar age of 5-11 Myr. Thirteen sources were detected in the 880 micron dust continuum at >3 sigma with inferred dust masses between 0.3 and 52 Mearth. The dust masses tend to be higher around the more massive stars, but the significance is marginal in that the probability of no correlation is p ~ 0.03. The evolution in the dust content in …
To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy…
High-precision photometry from space-based missions such as K2 and TESS enables detailed studies of young star variability. However, because space-based observing campaigns are often short (e.g., 80 days for K2), complementary long-baseline photometric surveys are critical for obtaining a complete understanding of young star variability, which can change on timescales of minutes to years. We therefore present and analyze light curves of members of the Upper Scorpius association made over 5.5 years by the ground-based Kilodegree Extremely Little Telescope (KELT), which complement the high-preci…
The star HD144548 (=HIP~78977; TYP~6212-1273-1) has been known as a detached eclipsing binary and a bona-fide member of the Upper Scorpius OB association. Continuous photometry from the K2 mission on Campaign Two has revealed the presence of additional eclipses due to the presence of a third star in the system. These are explained by a system composed of the two previously known members of the eclipsing system (Ba and Bb) with a period of 1.63 d, orbiting around an F7-F8V star with a period of 33.945 +/- 0.002 d in an eccentric orbit (e_A = 0.2652 +/- 0.0003). The timing of the eclipses of Ba …
We present projected rotational velocities for 20 early-type (B8-A9) and 74 late-type (F2-M8) members of the ~5 Myr old Upper Scorpius OB Association derived from high dispersion optical spectra obtained with the High Resolution Echelle Spectrometer (HIRES) on Keck I and the Magellan Inamori Kyocera Echelle (MIKE) on the Magellan Clay telescope. The spectroscopic sample is composed of stars and brown dwarfs with infrared signatures of circumstellar disks, both primordial and debris, and non-excess sources of comparable spectral type. We merge projected rotational velocities, accretion diagnost…
Pulsating B stars in the Scorpius-Centaurus Association with TESS
Indian Institute of Technology Roorkee（印度理工学院鲁尔基分校）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天文研究所）；Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文学系恒星天体物理学中心）；Astronomical Institute, Graduate School of Science, Tohoku University（东北大学理学研究科天文学研究所）
When determining absolute ages of identifiably young stellar populations, results strongly depend on which stars are studied. Cooler (K, M) stars typically yield ages that are systematically younger than warmer (A, F, G) stars by a factor of two. I explore the possibility that these age discrepancies are the result of magnetic inhibition of convection in cool young stars by using magnetic stellar evolution isochrones to determine the age of the Upper Scorpius subgroup of the Scorpius-Centaurus OB Association. A median age of 10 Myr consistent across spectral types A through M is found, except …
Stellar associations can be discerned as overdensities of sources not only in the physical space but also in the velocity space. The common motion of their members, gradually eroded by the galactic tidal field, is partially reminiscent of the initial kinematic structure. Using recent data from Gaia EDR3, combined with radial velocities from GALAH and APOGEE, we traced back the present positions of stars belonging to Upper Scorpius, a subgroup of Scorpius-Centaurus, the nearest OB association. About one half of the subgroup (the "clustered" population) appears composed of many smaller entities,…
We present deep 1.2 millimeter photometry of 37 stars in the young (5 Myr) Upper Scorpius OB association, sensitive to ~4 x 10^-3 Mjup of cool millimeter dust. Disks around four low- and solar-mass stars are detected, as well as one debris disk around an intermediate mass star, with dust masses ranging from 3.6 x 10^-3 -- 1.0 x 10^-1 Mjup. The source with the most massive disk exhibits a transition-disk spectral energy distribution. Combining our results with previous studies, we find the millimeter-detection fraction of Class II sources has significantly decreased from younger ages, and compa…
We report the results of a study of archival SuperWASP light curves for stars in Scorpius-Centaurus (Sco-Cen), the nearest OB association. We use SuperWASP time-series photometry to extract rotation periods for 189 candidate members of the Sco-Cen complex, and verify that 162 of those are members of the classic Sco-Cen subgroups of Upper Scorpius (US), Upper Centaurus-Lupus (UCL), and Lower Centaurus-Crux (LCC). This study provides the first measurements of rotation periods explicitly for large samples of pre-main sequence (pre-MS) stars spanning the UCL and LCC subgroups. Our final sample of …
We have investigated the brown dwarf (BD) and stellar disc fractions in the Upper Scorpius OB Association (USco) and compared them with several other young regions. We have compiled the most complete sample of of all spectroscopically confirmed BDs in USco, and have made use of the WISE catalog to identify the disc candidates. We report on the discovery of 12 new BD discs in USco, with spectral type (SpT) between M6 and M8.5. The WISE colors for the new discs are similar to the primordial (transition) discs earlier detected in USco. Combining with previous surveys, we find the lowest inner dis…
We present the first spatially resolved scattered-light images of four debris disks around members of the Scorpius-Centaurus (Sco-Cen) OB Association with high-contrast imaging and polarimetry using the Gemini Planet Imager (GPI). All four disks are resolved for the first time in polarized light and one disk is also detected in total intensity. The three disks imaged around HD 111161, HD 143675, and HD 145560 are symmetric in both morphology and brightness distribution. The three systems span a range of inclinations and radial extents. The disk imaged around HD 98363 shows indications of asymm…
Young multiple star systems provide excellent testing grounds for theories of star formation and evolution. EPIC 203868608 was previously studied~\citep{David2016} as a triple star system in the Upper Scorpius OB association, but the follow-up Keck NIRC2/HIRES/NIRSPAO observations reported here reveal its quadruple nature. We find that the system consists of a double-lined spectroscopic binary (SB2) Aab (M5+M5) and an eclipsing binary (EB) Bab with a total mass that is lower than that of the SB2. Furthermore, we measure the obliquity of the EB using the Doppler tomography technique during the …
The nearest region of massive star formation - the Scorpius-Centaurus OB2 association (Sco-Cen) - is a local laboratory ideally suited to the study of a wide range of astrophysical phenomena. Precision astrometry from the Gaia mission has expanded the census of this region by an order of magnitude. However, Sco-Cen's vastness and complex substructure make kinematic analysis of its traditional three regions, Upper Scorpius, Upper Centaurus-Lupus and Lower Centaurus-Crux, challenging. Here we use Chronostar, a Bayesian tool for kinematic age determination, to carry out a new kinematic decomposit…
We aim at constraining evolutionary models at low mass and young ages by identifying interesting transiting system members of the nearest OB association to the Sun, Upper Scorpius, targeted by the Kepler mission. We produced light curves for M dwarf members of the USco region surveyed during the second campaign of the Kepler K2 mission. We identified 'by eye' a transiting system, UScoJ161630.68-251220.1 (=EPIC203710387) with a combined spectral type of M5.25 whose photometric, astrometric, and spectroscopic properties makes it a member of USco. We conducted an extensive photometric and spectro…
The reality of a field Argus Association has been doubted in some papers in the literature. We apply Gaia DR2 data to stars previously suggested to be Argus members and conclude that a true association exists with age 40-50 Myr and containing many stars within 100 pc of Earth; Beta Leo and 49 Cet are two especially interesting members. Based on youth and proximity to Earth, Argus is one of the better nearby moving groups to target in direct imaging programs for dusty debris disks and young planets.
We present a kinematic study of the Scorpius-Centaurus (Sco-Cen) OB association (Sco OB2) using Gaia DR1 parallaxes and proper motions. Our goal is to test the classical theory that OB associations are the expanded remnants of dense and compact star clusters disrupted by processes such as residual gas expulsion. Gaia astrometry is available for 258 out of 433 members of the association, with revised Hipparcos astrometry used for the remainder. We use this data to confirm that the three subgroups of Sco-Cen are gravitationally unbound and have non-isotropic velocity dispersions, suggesting they…
We confirm and characterize a close-in ($P_{\rm{orb}}$ = 5.425 days), super-Neptune sized ($5.04^{+0.34}_{-0.37}$ Earth radii) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main sequence (11 Myr-old) star in the Upper Scorpius subgroup of the Scorpius-Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (<20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet's properties and con…
We utilize spectroscopically derived model atmosphere parameters and the \ion{Li}{1} $\lambda6104$ subordinate line and the $\lambda6708$ doublet to derive lithium abundances for 12 members of the Upper-Centaurus Lupus (UCL) and Lower-Centaurus Crux (LCC) subgroups of the Scorpius Centaurus OB Association. The results indicate any intrinsic Li scatter in our 0.9-1.4 $M_{\odot}$ stars is limited to ${\sim}0.15$ dex, consistent with the lack of dispersion in ${\ge}1.0$ $M_{\odot}$ stars in the 100 Myr Pleiades and 30-50 Myr IC 2391 and 2602 clusters. Both ab initio uncertainty estimates and the …
We have spectroscopically identified about 100 G-, K- and M-type members of the Scorpius Centaurus complex. To deduce the age of these young stars we compare their Li $λ$6708 absorption line strengths against those of stars in the TW Hydrae association and $β$ Pictoris moving group. These line strengths indicate that Sco-Cen stars are younger than $β$ Pic stars whose ages of ~12 Myr have previously been derived from a kinematic traceback analysis. Our derived age,~10Myr, for stars in the LCC and UCL subgroups of ScoCen is younger than previously published ages based on the moving cluster metho…
We present light curves and periodograms for 27 stars in the young Upper Scorpius association (age=$11 \pm 1$\,Myr) obtained with the Kepler spacecraft. This association is only the second stellar grouping to host several pulsating pre-main sequence (PMS) stars which have been observed from space. From an analysis of the periodograms, we identify six $δ$~Scuti variables and one $γ$~Doradus star. These are most likely PMS stars or else very close to the zero-age main sequence. Four of the $δ$~Scuti variables were observed in short-cadence mode, which allows us to resolve the entire frequency sp…
We present detailed modeling of the spatial distributions of gas and dust in 57 circumstellar disks in the Upper Scorpius OB Association observed with ALMA at sub-millimeter wavelengths. We fit power-law models to the dust surface density and CO $J$ = 3-2 surface brightness to measure the radial extent of dust and gas in these disks. We found that these disks are extremely compact: the 25 highest signal-to-noise disks have a median dust outer radius of 21 au, assuming an $R^{-1}$ dust surface density profile. Our lack of CO detections in the majority of our sample is consistent with these smal…
We found that multi-periodic low-mass stars discovered by Kepler K2 in the Upper Scorpius association are close binaries with typical separations of the order of 10 au and large mass ratios. These stars were surveyed by speckle interferometry at the SOAR telescope with spatial resolution of 0.04". Out of 129 observed targets, we resolved 70 pairs (including 16 previously known ones and three new triple systems). The distribution of projected separations of binaries with primary stars less massive than the Sun corresponds to a log-normal with median of 11.6 au and logarithmic dispersion of 0.60…
We present results of a spectroscopic survey for new K- and M-type members of Scorpius-Centaurus (Sco-Cen), the nearest OB Association (~100-200 pc). Using an X-ray, proper motion and color-magnitude selected sample, we obtained spectra for 361 stars, for which we report spectral classifications and Li and Halpha equivalent widths. We identified 156 new members of Sco-Cen, and recovered 51 previously published members. We have combined these with previously known members to form a sample of 493 solar-mass (~0.7-1.3 Msun) members of Sco-Cen. We investigated the star-formation history of this sa…
We present an analysis of the ages and star-formation history of the F-type stars in the Upper Scorpius (US), Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC) subgroups of Scorpius-Centaurus. We find that 1) our empirical isochrones are consistent with the previously published age-rank of the Sco-Cen subgroups, 2) LCC and UCL appear to reach the main sequence turn-on at spectral types ~F4 and ~F2, respectively. An analysis of the A-type stars shows US reaching the main sequence at about spectral type ~A3. 3) The median ages for the pre-main sequence members of UCL and LCC are 16 Myr …
We have performed a survey for new members of the Upper Sco association that have circumstellar disks using mid-infrared photometry from the Wide-field Infrared Survey Explorer (WISE). Through optical and near-infrared spectroscopy, we have confirmed 185 candidates as likely members of Upper Sco with spectral types ranging from mid-K to M9. They comprise ~36% of the known disk-bearing members of the association. We also have compiled all available mid-infrared photometry from WISE and the Spitzer Space Telescope for the known members of Upper Sco, resulting in a catalog of data for 1608 object…
We present the results of a deep ZYJ near-infrared survey of 13.5 square degrees in the Upper Scorpius (USco) OB association. We photometrically selected ~100 cluster member candidates with masses in the range 30-5 Jupiters, according to state-of-the-art evolutionary models. We identified 67 ZYJ candidates as bona-fide members, based on complementary photometry and astrometry. We also extracted five candidates detected with VISTA at YJ-only. One is excluded using deep optical z-band imaging, while two are likely non-members, and three remain as potential members. We conclude that the USco mass…
We propose 35 star systems within ~70 pc of Earth as newly identified members of nearby young stellar kinematic groups; these identifications include the first A- and late-B type members of the AB Doradus moving group and field Argus Association. All but one of the 35 systems contain a bright solar- or earlier-type star that should make an excellent target for the next generation of adaptive optics (AO) imaging systems on large telescopes. AO imaging has revealed four massive planets in orbit around the λ Boo star HR 8799. Initially the planets were of uncertain mass due in large part to the u…
Flares are known to play an important role for the evolution of the atmospheres of young planets. In order to understand the evolution of planets, it is thus important to study the flare-activity of young stars. This is particularly the case for young M-stars, because they are very active. We study photometrically and spectroscopically the highly active M-star 2MASS J16111534-1757214. We show that it is a member of the Upper Sco OB association, which has an age of 5-10 Myrs. We also re-evaluate the status of other bona-fide M-stars in this region and identify 42 members. Analyzing the K2-light…
We searched for binary companions to 20 young brown dwarfs in the Upper Scorpius association (145 pc, 5 Myr, nearest OB association) with the the Laser Guide Star adaptive optics system and the facility infrared camera NIRC2 on the 10 m Keck II telescope. We discovered a 0.14" companion (20.9+-0.4 AU) to the <0.1 MSun object SCH J16091837-20073523. From spectral deconvolution of integrated-light near-IR spectroscopy of SCH1609 using the SpeX spectrograph (Rayner et al. 2003), we estimate primary and secondary spectral types of M6+-0.5 and M7+-1.0, corresponding to masses of 79+-17 MJup and 55+…
We present 237 new spectroscopically confirmed pre-main-sequence K and M-type stars in the young Upper Scorpius subgroup of the Sco-Cen association, the near- est region of recent massive star formation. Using the Wide-Field Spectrograph at the Australian National University 2.3 m telescope at Siding Spring, we observed 397 kinematically and photometrically selected candidate members of Upper Scorpius, and identified new members by the presence of Lithium absorption. The HR-diagram of the new members shows a spread of ages, ranging from ~3-20 Myr, which broadly agrees with the current age esti…
We have refined the census of stars and brown dwarfs in the Upper Sco association (~10 Myr, ~145 pc) by 1) updating the selection of candidate members from our previous survey to include the high-precision astrometry from the second data release of Gaia, 2) obtaining spectra of a few hundred candidate members to measure their spectral types and verify their youth, and 3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward Upper Sco that show evidence of youth in this work and previous studies. We arrive at a catalog of 1761 objects that are adopted as members of Upper …
We measure the photometric rotation periods of the components of multiple systems in young stellar associations to investigate the causes of the observed rotation period dispersion. We present the case of the wide binary AG Tri in the 23-Myr young beta Pictoris Association consisting of K4 + M1 dwarfs. Our multi-band, multi-season photometric monitoring allowed us to measure the rotation periods of both components P_A = 12.4d and P_B = 4.66d, to detect a prominent magnetic activity in the photosphere, likely responsible for the measured radial velocity variations, and for the first time, a fla…
We present the results of photometric and spectroscopic follow-ups of the lowest mass member candidates in the nearest OB association, Upper Scorpius (5-10 Myr; 145+/-17 pc), with the Gran Telescopio de Canarias (GTC) and European Southern Observatory (ESO) Very Large Telescope (VLT). We confirm the membership of the large majority (>80%) of the candidates selected originally photometrically and astrometrically based on their spectroscopic features, weak equivalent widths of gravity-sensitive doublets, and radial velocities. Confirmed members follow a sequence over a wide magnitude range (J=17…
The nature and origin of free-floating planets (FFPs) are still largely unconstrained because of a lack of large homogeneous samples to enable a statistical analysis of their properties. So far, most FFPs have been discovered using indirect methods; microlensing surveys have proved particularly successful to detect these objects down to a few Earth masses. However, the ephemeral nature of microlensing events prevents any follow-up observations and individual characterization. Several studies have identified FFPs in young stellar clusters and the Galactic field but their samples are small or he…
We present Herschel PACS photometry of seventeen B- to M-type stars in the 30 Myr-old Tucana-Horologium Association. This work is part of the Herschel Open Time Key Programme "Gas in Protoplanetary Systems" (GASPS). Six of the seventeen targets were found to have infrared excesses significantly greater than the expected stellar IR fluxes, including a previously unknown disk around HD30051. These six debris disks were fitted with single-temperature blackbody models to estimate the temperatures and abundances of the dust in the systems. For the five stars that show excess emission in the Hersche…
Spectroscopic follow-up is a pre-requisite for studies of the formation and early evolution of brown dwarfs. Here we present IRTF/SpeX near-infrared spectroscopy of 30 candidate members of the young Upper Scorpius association, selected from our previous survey work. All 24 high confidence members are confirmed as young very low mass objects with spectral types from M5 to L1, 15-20 of them are likely brown dwarfs. This high yield confirms that brown dwarfs in Upper Scorpius can be identified from photometry and proper motions alone, with negligible contamination from field objects (<4%). Out of…
We present a census of the disk population for UKIDSS selected brown dwarfs in the 5-10 Myr old Upper Scorpius OB association. For 116 objects originally identified in UKIDSS, the majority of them not studied in previous publications, we obtain photometry from the WISE database. The resulting colour-magnitude and colour-colour plots clearly show two separate populations of objects, interpreted as brown dwarfs with disks (class II) and without disks (class III). We identify 27 class II brown dwarfs, 14 of them not previously known. This disk fraction (27 out of 116 or 23%) among brown dwarfs wa…
We present the results of a long term orbit monitoring program, using sparse aperture masking observations taken with NIRC2 on the Keck-II telescope, of seven G to M-type members of the Upper Scorpius subgroup of the Sco-Cen OB association. We present astrometry and derived orbital elements of the binary systems we have monitored, and also determine the age, component masses, distance and reddening for each system using the orbital solutions and multi-band photometry, including Hubble Space Telescope photometry, and a Bayesian fitting procedure. We find that the models can be forced into agree…
HD 61005 is a nearby young solar type star that shows a large infrared excess due to a debris disk. The disk has been recently imaged from ground and space, with indications of several components. Some characteristics of the disk suggest the presence of planetary companions around the star, that remain undetected in deep adaptive optics imaging. For a better understanding of the system we aim to refine the determination of the stellar parameters, with emphasis on the stellar age and system orientation. We used ASAS and Hipparcos photometry and FEROS spectra to determine the rotation period, ra…
We present new z- and H-band photometry and proper motion measurements for the five candidate very-low-mass T-type objects we recently proposed to be members of the nearest OB association to the Sun, Upper Scorpius. These new data fail to corroborate our prior conclusions regarding their spectral types and affiliation with the Upper Scorpius population. We conclude that we may be in presence of a turnover in the mass function of Upper Sco taking place below 10-4 Jupiter masses, depending on the age assigned to Upper Sco and the models used.
The Upper-Scorpius association (5-11 Myr) contains a unique population of low-mass (M<30 MJup) brown-dwarfs. The detailed relative characterization of their physical properties (mass, radius, temperature, composition, ongoing accretion) offers the opportunity to potentially explore their origin and their mechanisms of formation. We aim at characterizing the chemical and physical properties of three young, late-M brown-dwarfs claimed to be companions of the Upper-Scorpius stars USco161031.9-16191305, HIP77900, and HIP78530 using medium resolution spectroscopy at UV (R~3300), optical (R~5400), a…
To address the statistics of binary stars in the 8-Myr old Upper Scorpius star formation region, we conducted speckle-interferometric survey of 614 association members more massive than 0.4 Msun (spectral types earlier than M3V) based on the list of Luhman et al. (2018). We resolved 187 pairs, 55 of those are new discoveries. Using also the published data and the Gaia DR2, a catalog of 250 physical binaries is produced. We carefully estimated detection limits for each target and studied binary statistics in the separation range from 0.06" to 20" (9 to 2800 au), as well as clustering at larger …
Using VLT/SPHERE near-infrared dual-band imaging and integral field spectroscopy we discovered an edge-on debris disk around the 17\,Myr old A-type member of the Scorpius-Centaurus OB association HD 110058. The edge-on disk can be traced to about 0.6" or 65 AU projected separation. In its northern and southern wings, the disk shows at all wavelengths two prominent, bright and symmetrically placed knots at 0.3" or 32 AU from the star. We interpret these knots as a ring of planetesimals whose collisions may produce most of the dust observed in the disk. We find no evidence for a bow in the disk,…
