We present the results of a proper motion wide-field near-infrared survey of the entire Upper Sco (USco) association (∼160 square degrees) released as part of the United Kingdom Infrared Telescope ...Infrared Deep Sky (UKIDSS) Galactic Clusters Survey (GCS) Data Release 10 (DR10). We have identified a sample of ∼400 astrometric and photometric member candidates combining proper motions and photometry in five near-infrared passbands and another 286 with HK photometry and 2MASS/GCS proper motions. We also provide revised membership for all previously published USco low-mass stars and substellar members based on our selection and identify new candidates, including in regions affected by extinction. We find negligible variability between the two K-band epochs, below the 0.06 mag rms level. We estimate an upper limit of 2.2 per cent for wide common proper motions with projected physical separations less than ∼15 000 au. We derive a disc frequency for USco low-mass stars and brown dwarfs between 26 and 37 per cent, in agreement with estimates in IC 348 and σ Ori. We derive the mass function of the association and find it consistent with the (system) mass function of the solar neighbourhood and other clusters surveyed by the GCS in the 0.2-0.03 M mass range. We confirm the possible excess of brown dwarfs in USco.
Aims. Our scientific goal is to provide revised membership lists of the α Per, Pleiades, and Praesepe clusters exploiting the second data release of Gaia and produce five-dimensional maps (α, δ, π, ...μα cos δ, μδ) of these clusters. Methods. We implemented the kinematic method combined with the statistical treatment of parallaxes and proper motions to identify astrometric member candidates of three of the most nearby and best studied open clusters in the sky. Results. We cross-correlated the Gaia catalogue with large-scale public surveys to complement the astrometry of Gaia with multi-band photometry from the optical to the mid-infrared. We identified 517, 1248, and 721 bona fide astrometric member candidates inside the tidal radius of α Per, the Pleiades, and Praesepe, respectively. We cross-matched our final samples with catalogues from previous surveys to address the level of completeness. We update the main physical properties of the clusters, including mean distance and velocity, as well as core, half-mass, and tidal radii. We infer updated ages from the white dwarf members of the Pleiades and Praesepe. We derive the luminosity and mass functions of the three clusters and compare them to the field mass function. We compute the positions in space of all member candidates in the three regions to investigate their distribution in space. Conclusions. We provide updated distances and kinematics for the three clusters. We identify a list of members in the α Per, Pleiades, and Praesepe clusters from the most massive stars all the way down to the hydrogen-burning limit with a higher confidence and better astrometry than previous studies. We produce complete 5D maps of stellar and substellar bona fide members in these three regions. The photometric sequences derived in several colour–magnitude diagrams represent benchmark cluster sequences at ages from 90 to 600 Myr. We note the presence of a stream around the Pleiades cluster extending up to 40 pc from the cluster centre.
ABSTRACT
We aim at identifying very low-mass isolated planetary-mass member candidates in the nearest OB association to the Sun, Upper Scorpius (USco) (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 multiband (Y = 21.2, J = 20.5, Z = 22.0 mag) photometric survey of 6 deg2 in the central region of USco. 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 predicted masses below 5 Jupiter masses, well into the planetary-mass regime. We extracted a sample of 57 candidates in this area and present infrared spectroscopy confirming two of them as young L-type members with characteristic spectral features of 10-Myr-old brown dwarfs. Among the 57 candidates, we highlight 10 new candidates fainter than the coolest members previously confirmed spectroscopically. We do not see any obvious sign of decrease in the mass spectrum of the association, suggesting that star processes can form substellar objects with masses down to 4–5 Jupiter masses.
Aims. Our scientific goal is to provide a 3D map of the nearest open cluster to the Sun, the Hyades, combining the recent release of Gaia astrometric data, ground-based parallaxes of sub-stellar ...member candidates and photometric data from surveys which cover large areas of the cluster. Methods. We combined the second Gaia release with ground-based H-band parallaxes obtained with the infrared camera on the 2 m robotic Liverpool telescope to astrometrically identify stellar and sub-stellar members of the Hyades, the nearest open cluster to the Sun. Results. We find 1764 objects within 70° radius from the cluster centre from the Gaia second data release, whose kinematic properties are consistent with the Hyades. We limit our study to 30 pc from the cluster centre (47.03 ± 0.20 pc) where we identify 710 candidate members, including 85 and 385 in the core and tidal radius, respectively. We determine proper motions and parallaxes of eight candidate brown dwarf members and confirm their membership. Using the 3D positions and a model-based mass-luminosity relation we derive a luminosity and mass function in the 0.04–2.5 M⊙ range. We confirm evidence for mass segregation in the Hyades and find a dearth of brown dwarfs in the core of the cluster. From the white dwarf members we estimate an age of 640 −49+67 − 49 + 67 $ ^{+67}_{-49} $ Myr. Conclusions. We identify a list of members in the Hyades cluster from the most massive stars down to the brown dwarfs. We produce for the first time a 3D map of the Hyades cluster in the stellar and sub-stellar regimes and make available the list of candidate members.
The UKIRT Infrared Deep Sky Survey (UKIDSS) Lawrence, A.; Warren, S. J.; Almaini, O. ...
Monthly Notices of the Royal Astronomical Society,
08/2007, Volume:
379, Issue:
4
Journal Article
Peer reviewed
Open access
We describe the goals, design, implementation, and initial progress of the UKIRT Infrared Deep Sky Survey (UKIDSS), a seven-year sky survey which began in 2005 May. UKIDSS is being carried out using ...the UKIRT Wide Field Camera (WFCAM), which has the largest étendue of any infrared astronomical instrument to date. It is a portfolio of five survey components covering various combinations of the filter set ZYJHK and H2. The Large Area Survey, the Galactic Clusters Survey, and the Galactic Plane Survey cover approximately 7000 deg2 to a depth of K∼ 18; the Deep Extragalactic Survey covers 35 deg2 to K∼ 21, and the Ultra Deep Survey covers 0.77 deg2 to K∼ 23. Summed together UKIDSS is 12 times larger in effective volume than the 2MASS survey. The prime aim of UKIDSS is to provide a long-term astronomical legacy data base; the design is, however, driven by a series of specific goals – for example, to find the nearest and faintest substellar objects, to discover Population II brown dwarfs, if they exist, to determine the substellar mass function, to break the z= 7 quasar barrier; to determine the epoch of re-ionization, to measure the growth of structure from z= 3 to the present day, to determine the epoch of spheroid formation, and to map the Milky Way through the dust, to several kpc. The survey data are being uniformly processed. Images and catalogues are being made available through a fully queryable user interface – the WFCAM Science Archive (http://surveys.roe.ac.uk/wsa). The data are being released in stages. The data are immediately public to astronomers in all ESO member states, and available to the world after 18 months. Before the formal survey began, UKIRT and the UKIDSS consortia collaborated in obtaining and analysing a series of small science verification (SV) projects to complete the commissioning of the camera. We show some results from these SV projects in order to demonstrate the likely power of the eventual complete survey. Finally, using the data from the First Data Release, we assess how well UKIDSS is meeting its design targets so far.
Abstract
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 per cent) of candidates originally selected 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 = 17.0–19.3 mag) in several colour–magnitude diagrams with optical, near- and mid-infrared photometry and have near-infrared spectral types in the L1–L7 interval with likely masses below 15 Jupiter masses. We find that optical spectral types tend to be earlier than near-infrared spectral types by a few subclasses for spectral types later than M9. We investigate the behaviour of spectral indices, defined in the literature as a function of spectral type and gravity, by comparison with values reported in the literature for young and old dwarfs. We also derive effective temperatures in the 1900–1600 K range from fits of synthetic model-atmosphere spectra to the observed photometry, but we caution that the procedure carries large uncertainties. We determine bolometric corrections for young L dwarfs with ages of ∼5–10 Myr (Upper Sco association) and find them to be similar in the J band but larger by 0.1–0.4 mag in the K band with respect to field L dwarfs. Finally, we discover two faint young L dwarfs, Visible and Infrared Survey Telescope for Astronomy (VISTA) J1607−2146 (L4.5) and VISTA J1611−2215 (L5), that have Hα emission and possible flux excesses at 4.5 μm, pointing to the presence of accretion from a disc on to the central objects of mass below ∼15MJup at an age of 5–10 Myr.
The Euclid spacecraft has been launched and will carry out a deep survey benefiting the discovery and characterisation of ultracool dwarfs (UCDs), especially in the Euclid Deep Fields (EDFs), which ...the telescope will scan repeatedly throughout its mission. The photometric and spectroscopic standards
in the EDFs are important benchmarks, crucial for the classification and characterisation of new UCD discoveries and for the calibration of the mission itself. We aim to provide a list of photometric UCD candidates and collect near-infrared reconnaissance spectra for M, L, and T-type UCDs in the EDFs as future $Euclid$ UCD references. In EDF North, we cross-matched public optical and infrared surveys with certain photometric criteria to select UCDs. In EDF Fornax and EDF South, we used photometrically classified samples from the literature. We also include UCDs identified by Gaia DR2.
We selected seven UCD targets with different spectral types from the lists and obtained low-resolution 0.9--2.5 mu m spectra of them using GTC/EMIR and the VLT/X-shooter. We also selected a young, bright L dwarf near EDF Fornax to test the coherence of these two facilities. We included one extra T dwarf in EDF North with its published $J$-band spectrum. We retrieved a list of 92 (49, 231) M, 33 (29, 115) L, and one (0, 2) T dwarf candidates in EDF North, Fornax, and South, respectively. They are provided to guide future UCD discoveries and characterisations by $Euclid$.
In total, we collected near-infrared spectra for nine UCDs, including two M types, three L types, and four T types in or close to the three EDFs.
The Euclidised spectra show consistency in their spectral classification, which demonstrates that slitless Euclid spectroscopy will recover the spectral types with high fidelity for UCDs, both in the EDFs and in the wide survey. We also demonstrate that Euclid will be able to distinguish different age groups of UCDs.
We report the results from a photometric and spectroscopic survey of ∼1.4 deg2 of the young open cluster IC 2602. Fourteen objects have been identified as having magnitudes, spectral types and radial ...velocities consistent with being probable or possible low-mass stellar members of the cluster. We have used the observed location of the lithium depletion boundary in the sequence defined by these objects to place a new and improved constraint on the cluster age, τ= 46+6−5 Myr. This new determination is larger by a factor ∼1.3–1.8 than the majority of age estimates which have been obtained using the main-sequence turn-off or pre-main-sequence isochrone techniques. It is thus consistent with the trend indicated by the results of similar studies on other young open clusters. Based on this new age, we set a lower limit on the cluster mass function over the range M = 0.054 − 0.24 M⊙, dn/dM > 46 M−1⊙. If the mass function of IC 2602 has a form similar to that of other young clusters and associations then future wide, deep surveys can expect to unearth at least a handful of brown dwarfs which could potentially serve as benchmark objects.
ABSTRACT
The theory of substellar evolution predicts that there is a sharp mass boundary between lithium and non-lithium brown dwarfs, not far below the substellar-mass limit. The imprint of ...thermonuclear burning is carved on the surface lithium abundance of substellar-mass objects during the first few hundred million years of their evolution, leading to a sharp boundary between lithium and non-lithium brown dwarfs, so-called, the lithium test. The theoretical predictions can be tested by comparing with observations of lithium in the individual components of binaries with dynamical masses measured from orbital motions. New optical spectroscopic observations of the binaries DENIS J063001.4−184014AB and DENIS J225210.7−173013AB obtained using the 10.4-m Gran Telescopio de Canarias are reported here. They allow us to re-determine their combined optical spectral types (M9.5 and L6.5, respectively) and to search for the presence of the Li i resonance doublet. The non-detection of the Li i feature in the combined spectrum of DENIS J063001.4−184014AB is converted into estimates for the depletion of lithium in the individual components of this binary system. In DENIS J225210.7−173013AB, we report the detection of a weak Li i feature which we tentatively ascribe as arising from the contribution of the T3.5-type secondary. Combining our results with data for seven other brown dwarf binaries in the literature treated in a self-consistent way, we confirm that there is indeed a sharp transition in mass for lithium depletion in brown dwarfs, as expected from theoretical calculations. We estimate such mass boundary is observationally located at 51.48$^{+0.22}_{-4.00}\, M_\mathrm{Jup}$, which is lower than the theoretical determinations.
The star HD 144548 (=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 (eA = 0.2652 ± 0.0003). The timing of the eclipses of Ba and Bb reveals the same 33.9 d periodicity, which we interpret as the combination of a light time effect combined with dynamical perturbations on the close system. Here we combine radial velocities and analytical approximations for the timing of the eclipses to derive masses and radii for the three components of the system. We obtain a mass of 1.44 ± 0.04 M⊙ and radius of 2.41 ± 0.03 R⊙ for the A component, and almost identical masses and radii of about 0.96 M⊙ and 1.33 R⊙ for each of the two components of the close binary. HD 144548 is the first triply eclipsing system for which radial velocities of all components could be measured.
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