Context. Selecting a cluster in proper motion space is an established method for identifying members of a star-forming region. The first data release from Gaia (DR1) provides an extremely large and ...precise stellar catalogue, which when combined with the Tycho-2 catalogue gives the 2.5 million parallaxes and proper motions contained within the Tycho-Gaia Astrometric Solution (TGAS). Aims. We aim to identify new member candidates of the nearby Upper Scorpius subgroup of the Scorpius-Centaurus Complex within the TGAS catalogue. In doing so, we also aim to validate the use of a density-based clustering algorithm (DBSCAN) on spatial and kinematic data as a robust member selection method. Methods. We constructed a method for member selection using a density-based clustering algorithm (DBSCAN) applied over proper motion and distance. We then applied this method to Upper Scorpius and evaluated the results and performance of the method. Results. We identified 167 member candidates of Upper Scorpius, of which 78 are new, distributed within a 10° radius from its core. These member candidates have a mean distance of 145.6 ± 7.5 pc and a mean proper motion of (−11.4, −23.5) ± (0.7, 0.4) mas yr−1. These values are consistent with measured distances and proper motions of previously identified bona fide members of the Upper Scorpius association.
Context. The Ophiuchus cloud complex is one of the best laboratories to study the earlier stages of the stellar and protoplanetary disc evolution. The wealth of accurate astrometric measurements ...contained in the Gaia Data Release 2 can be used to update the census of Ophiuchus member candidates. Aims. We seek to find potential new members of Ophiuchus and identify those surrounded by a circumstellar disc. Methods. We constructed a control sample composed of 188 bona fide Ophiuchus members. Using this sample as a reference we applied three different density-based machine learning clustering algorithms (DBSCAN, OPTICS, and HDBSCAN) to a sample drawn from the Gaia catalogue centred on the Ophiuchus cloud. The clustering analysis was applied in the five astrometric dimensions defined by the three-dimensional Cartesian space and the proper motions in right ascension and declination. Results. The three clustering algorithms systematically identify a similar set of candidate members in a main cluster with astrometric properties consistent with those of the control sample. The increased flexibility of the OPTICS and HDBSCAN algorithms enable these methods to identify a secondary cluster. We constructed a common sample containing 391 member candidates including 166 new objects, which have not yet been discussed in the literature. By combining the Gaia data with 2MASS and WISE photometry, we built the spectral energy distributions from 0.5 to 22 μm for a subset of 48 objects and found a total of 41 discs, including 11 Class II and 1 Class III new discs. Conclusions. Density-based clustering algorithms are a promising tool to identify candidate members of star forming regions in large astrometric databases. By combining the Gaia data with infrared catalogues, it is possible to discover new protoplanetary discs. If confirmed, the candidate members discussed in this work would represent an increment of roughly 40–50% of the current census of Ophiuchus.
Understanding disk evolution and dissipation is essential for studies of planet formation. Transition disks, i.e., disks with large dust cavities and gaps, are promising candidates of active ...evolution. About two dozen candidates, selected by their spectral energy distribution (SED), have been confirmed to have dust cavities through millimeter interferometric imaging, but this sample is biased toward the brightest disks. The Spitzer surveys of nearby low-mass star-forming regions have resulted in more than 4000 young stellar objects. Using color criteria, we selected a sample of ~150 candidates and an additional 40 candidates and known transition disks from the literature. The Spitzer data were complemented by new observations at longer wavelengths, including new JCMT and APEX submillimeter photometry, and WISE and Herschel-PACS mid- and far-infrared photometry. Furthermore, optical spectroscopy was obtained and stellar types were derived for 85% of the sample, including information from the literature. The SEDs were fit to a grid of RADMC-3D disk models with a limited number of parameters: disk mass, inner disk mass, scale height and flaring, and disk cavity radius, where the latter is the main parameter of interest. About 72% of our targets possibly have dust cavities based on the SED. The derived cavity sizes are consistent with imaging/modeling results in the literature, where available. Trends are found with Ldisk over L∗ ratio and stellar mass and a possible connection with exoplanet orbital radii. A comparison with a previous study where color observables are used reveals large overlap between their category of planet-forming disks and our transition disks with cavities. A large number of the new transition disk candidates are suitable for follow-up observations with ALMA.
Transitional discs are protoplanetary discs with opacity gaps/cavities in their dust distribution, a feature that may be linked to planet formation. We perform Bayesian modelling of the three ...transitional discs SZ Cha, CS Cha, and T25 including photometry from the Herschel Space Observatory to quantify the improvements added by these new data. We find disc dust masses between 2 × 10−5 and 4 × 10−4 M⊙ and gap radii in the range of 7–18 au, with uncertainties of ∼ one order of magnitude and ∼4 au, respectively. Our results show that adding Herschel data can significantly improve these estimates with respect to mid-infrared data alone, which have roughly twice as large uncertainties on both disc mass and gap radius. We also find weak evidence for different density profiles with respect to full discs. These results open exciting new possibilities to study the distribution of disc masses for large samples of discs.
Context. The silicate feature near 10 μm is one of the main tools available to study the mineralogy of circumstellar disks and envelopes, providing information on the thermal processing, growth, ...location, and circulation of dust grains. Aims. We investigate the silicate feature of the two Class I components of HH 250-IRS, a resolved binary system with a separation of 0″53 driving a Herbig-Haro flow. Each component has its own circumstellar envelope, and the system is surrounded by a circumbinary disk. Methods. We carried out low resolution spectroscopy in the 8–13 μm range using VISIR, the thermal infrared imager and spectrograph at ESO’s Very Large Telescope. Results. The silicate features of both sources are clearly different. The northwest (NW) component has a broad, smooth absorption profile lacking structure. We attribute most of it to foreground interstellar dust absorption, but estimate that additional absorption by amorphous silicates takes place in the circumstellar envelope of the young stellar object. The southeast (SE) component shows the silicate feature in emission, with structure longward of 9.5 μm indicating the presence of crystalline dust in the dominant form of forsterite. The apparent lack of an absorption feature caused by foreground dust is probably due to the filling of the band with emission by amorphous silicates in the envelope of the object. Conclusions. Despite their virtually certain coevality, the differences in the components of the HH 250-IRS binary are most likely due to markedly different circumstellar environments. The NW component displays an unevolved envelope, whereas dust growth and crystallization has taken place in the SE component. The weak or absent signatures of enstatite in the latter are fairly unusual among envelopes with crystalline dust, and we tentatively relate it to a possible wide gap or an inner truncation of the disk already hinted at in previous observations by a drop in the L′-band flux, which might indicate that the SE component could actually be a very close binary. We speculate that the clear differences between the silicate feature spectra of both components of HH 250-IRS may be due either to disk evolution sped up by multiplicity, or by accretion variability leading to episodes of crystal formation. Different inclinations with respect to the line of sight may play a role as well, although it is very unlikely that they are the sole element for the differences between both objects.
Context. New data from the Herschel Space Observatory are broadening our understanding of the physics and evolution of the outer regions of protoplanetary disks in star-forming regions. In particular ...they prove to be useful for identifying transitional disk candidates. Aims. The goals of this work are to complement the detections of disks and the identification of transitional disk candidates in the Lupus clouds with data from the Herschel Gould Belt Survey. Methods. We extracted photometry at 70, 100, 160, 250, 350, and 500 μm of all spectroscopically confirmed Class II members previously identified in the Lupus regions and analyzed their updated spectral energy distributions. Results. We have detected 34 young disks in Lupus in at least one Herschel band, from an initial sample of 123 known members in the observed fields. Using recently defined criteria, we have identified five transitional disk candidates in the region. Three of them are new to the literature. Their PACS-70 μm fluxes are systematically higher than those of normal T Tauri stars in the same associations, as already found in T Cha and in the transitional disks in the Chamaeleon molecular cloud. Conclusions. Herschel efficiently complements mid-infrared surveys for identifying transitional disk candidates and confirms that these objects seem to have substantially different outer disks than the T Tauri stars in the same molecular clouds.
We have identified four circumstellar disks with a deficit of dust emission from their inner 15-50 AU. All four stars have F-G spectral type and were uncovered as part of the Spitzer Space Telescope ..."Cores to Disks" Legacy Program Infrared Spectrograph (IRS) first-look survey of similar to 100 pre-main-sequence stars. Modeling of the spectral energy distributions indicates a reduction in dust density by factors of 100-1000 from disk radii between similar to 0.4 and 15-50 AU but with massive gas-rich disks at larger radii. This large contrast between the inner and outer disk has led us to use the term "cold disks" to distinguish these unusual systems. However, hot dust (0.02-0.2)- unk is still present close to the central star (R less than or equal to 0.8 AU). We introduce the 30 mu m/13 mu m flux density ratio as a new diagnostic for identifying cold disks. The mechanisms for dust clearing over such large gaps are discussed. Although rare, cold disks are likely in transition from an optically thick to an optically thin state and so offer excellent laboratories for the study of planet formation.
Context. Light curve modulations in the sample of Kepler planet candidates allows the disentangling of the nature of the transiting object by photometrically measuring its mass. This is possible by ...detecting the effects of the gravitational pull of the companion (ellipsoidal modulations) and in some cases, the photometric imprints of the Doppler effect when observing in a broad band (Doppler beaming). Aims. We aim to photometrically unveil the nature of some transiting objects showing clear light curve modulations in the phase-folded Kepler light curve. Methods. We selected a subsample among the large crop of Kepler objects of interest (KOIs) based on their chances to show detectable light curve modulations, i.e., close (a< 12 R sub(*)) and large (in terms of radius, according to their transit signal) candidates. We modeled their phase-folded light curves with consistent equations for the three effects, namely, reflection, ellipsoidal and beaming (known as REB modulations). Results. We provide detailed general equations for the fit of the REB modulations for the case of eccentric orbits. These equations are accurate to the photometric precisions achievable by current and forthcoming instruments and space missions. By using this mathematical apparatus, we find three close-in very low-mass companions (two of them in the brown dwarf mass domain) orbiting main-sequence stars (KOI-554, KOI-1074, and KOI-3728), and reject the planetary nature of the transiting objects (thus classifying them as false positives). In contrast, the detection of the REB modulations and transit/eclipse signal allows the measurement of their mass and radius that can provide important constraints for modeling their interiors since just a few cases of low-mass eclipsing binaries are known. Additionally, these new systems can help to constrain the similarities in the formation process of the more massive and close-in planets (hot Jupiters), brown dwarfs, and very low-mass companions.
Context.
MWC 758 is a young star surrounded by a transitional disk. The disk shows an inner cavity and spiral arms that could be caused by the presence of protoplanets. Recently, a protoplanet ...candidate has been detected around MWC 758 through high-resolution
L
′-band observations. The candidate is located inside the disk cavity at a separation of ~111 mas from the central star, and at an average position angle of ~165.5°.
Aims.
We aim at detecting accreting protoplanet candidates within the disk of MWC 758 through angular spectral differential imaging (ASDI) observations in the optical regime. In particular, we explore the emission at the position of the detected planet candidate.
Methods.
We have performed simultaneous adaptive optics observations in the H
α
line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT).
Results.
The data analysis does not reveal any H
α
signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5
σ
upper limit of ~7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a H
α
line luminosity of
L
H
α
≲ 5×10
−5
L
⊙
at 111 mas. Assuming that
L
H
α
scales with
L
acc
as in classical T Tauri stars (CTTSs) as a first approximation, we can estimate an accretion luminosity of
L
acc
< 3.7 × 10
−4
L
⊙
for the protoplanet candidate. For the predicted mass range of MWC 758b, 0.5–5
M
Jup
, this implies accretion rates smaller than
Ṁ
< 3.4 × (10
−8
−10
−9
)
M
⊙
yr
−1
, for an average planet radius of 1.1
R
Jup
. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for
R
in
= 1
R
Jup
. The ZIMPOL line luminosity is consistent with the H
α
upper limit predicted by these models for truncation radii ≲3.2
R
Jup
.
Conclusions.
The non-detection of any H
α
emitting source in the ZIMPOL images does not allow us to unveil the nature of the
L
′ detected source. Either it is a protoplanet candidate or a disk asymmetry.
Context. Many star forming regions are known to have associated dispersed populations, whose members are located away from known current star forming sites. Their origin is unclear, and any ...identification of the members through relatively short-lived signatures of youth can miss them. Aims. We aim at confirming membership of a sample of cool stars identified in a previous work in the Lupus 1, 3, and 4 clouds as candidate members. Most of them do not display near- or mid-infrared excess or any other easily recognizable signatures of youth. Methods. We use low-resolution spectroscopy in the red part of the spectrum, including the Hα region, to accurately determine spectral types and probe surface gravity-sensitive features that provide reliable criteria for distinguishing cool giant stars, young stellar objects, and evolved dwarf stars. Results. Most of the candidate members of a possible dispersed population around Lupus 1 are found to be background K or early M giants. However, about half of the observed members of Lupus 3 are confirmed as young objects, including both low-mass stars and brown dwarfs. The distributed population is compared to the sample of lightly obscured members projected closer to the densest parts of the Lupus 3 star forming cloud, and the estimated ages of the members of both sets are found to be consistent with a single distribution. However, we find statistical indications (although at a low significance level) of a decrease in the frequency of infrared excesses in the distributed population. Some nongiant members are also identified with gravity-sensitive features typical of more evolved stars, and we argue that these may belong to an older population associated with the Gould Belt, similar to what is observed in the direction of other nearby star forming regions. We also confirm two additional, very low-mass members of Lupus 4. Conclusions. Although some of its members have already been known previous to this work, our results emphasize the richness of the low-mass distributed population around Lupus 3 and the existence of much less numerous dispersed populations around Lupus 1 and Lupus 4. The apparent spatial segregation as a function of the abundance of circumstellar material favors dynamical ejection from the main star forming cloud as the mechanism that gives rise to the dispersed population.
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