- ID:
- ivo://CDS.VizieR/J/A+A/623/A23
- Title:
- Differential photometry of MML 53
- Short Name:
- J/A+A/623/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the most comprehensive analysis to date of the Upper Centaurus Lupus eclipsing binaryMML53 (with P_EB_=2.097892d), and for the first time, confirm the bound-nature of the third star (in a P_3_~9yr orbit) by constraining its mass dynamically. Our analysis is based on new and archival spectra and time-series photometry, spanning 80% of one orbit of the outer component. From the spectroscopic analysis, we determined the temperature of the primary star to be 4880+/-100K. The study of the close binary incorporated treatment of spots and dilution by the tertiary in the light curves, allowing for the robust measurement of the masses of the eclipsing components within 1% (M1=1.0400+/-0.0067M_{sun}_ and M2=0.8907+/-0.0058M_{sun}_), their radii within 4.5% (R1=1.283+/-0.043R_{sun}_ and R2=1.107+/-0.049R_{sun}_), and the temperature of the secondary star (T_eff,2_=4379+/-100K). From the analysis of the eclipse timings, and the change in systemic velocity of the eclipsing binary and the radial velocities of the third star, we measured the mass of the outer companion to be 0.7M_{sun}_ (with a 20% uncertainty). The age we derived from the evolution of the temperature ratio between the eclipsing components is fully consistent with previous, independent estimates of the age of Upper Centaurus Lupus (16+/-2Myr). At this age, the tightening of the MML53 eclipsing binary has already occurred, thus supporting close-binary formation mechanisms that act early in the stars' evolution. The eclipsing components of MML53 roughly follow the same theoretical isochrone, but appear to be inflated in radius (by 20% for the primary and 10% for the secondary) with respect to recent evolutionary models. However, our radius measurement of the 1.04M_{sun}_ primary star of MML53 is in full agreement with the independent measurement of the secondary of NP Per which has the same mass and a similar age. The eclipsing stars of MML53 are found to be larger but not cooler than predicted by non-magnetic models, it is not clear what is the mechanism that is causing the radius inflation given that activity, spots and/or magnetic fields slowing their contraction, require the inflated stars to be cooler to remain in thermal equilibrium.
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- ID:
- ivo://CDS.VizieR/J/A+A/625/A49
- Title:
- Dimming event of RW Aurigae A
- Short Name:
- J/A+A/625/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- RW Aur A is a classical T Tauri star that has suddenly undergone three major dimming events since 2010. The reason for these dimming events is still not clear. The two epochs of observations uploaded here are on the deep dimming events (2015) and immediate after the dimmin event (2016).
- ID:
- ivo://CDS.VizieR/J/A+A/624/A87
- Title:
- Discovery of a resolved disk around Wray 15-788
- Short Name:
- J/A+A/624/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Protoplanetary disks are the birth environments of planetary systems. Therefore, the study of young, circumstellar environments is essential to understanding the processes taking place in planet formation and the evolution of planetary systems. We detect and characterize circumstellar disks and potential companions around solar-type, pre-main sequence stars in the Scorpius-Centaurus association (Sco-Cen). As part of our ongoing survey we carried out high-contrast imaging with VLT/SPHERE/IRDIS to obtain polarized and total intensity images of the young (11^+16^_-7_)Myr old) K3IV star Wray 15-788 within the Lower Centaurus Crux subgroup of Sco-Cen. For the total intensity images, we remove the stellar halo via an approach based on reference star differential imaging in combination with principal component analysis. Both total intensity and polarimetric data resolve a disk around the young, solar-like Sco-Cen member Wray 15-788. Modeling of the stellar spectral energy distribution suggests that this is protoplanetary disk at a transition stage. We detect a bright outer ring at a projected separation of ~370mas (~56au), hints of inner substructures at ~170mas (~28au), and a gap in between. Within a position angle range of only 60{deg}<{phi}<240{deg}, we are confident at the 5{sigma} level that we detect actual scattered light flux from the outer ring of the disk; the remaining part is indistinguishable from background noise. For the detected part of the outer ring we determine a disk inclination of i=21{deg}+/-6{deg} and a position angle of {varphi}=76{deg}+/-16{deg}. Furthermore, we find that Wray 15-788 is part of a binary system with the A2V star HD 98363 at a separation of ~50arcsec (~6900,au). The detection of only half of the outer ring might be due to shadowing by a misaligned inner disk. A potential substellar companion can cause the misalignment of the inner structures and can be responsible for clearing the detected gap from scattering material.However, we cannot rule out the possibility of a non-detection due to our limited signal-to-noise ratio, combined with brightness azimuthal asymmetry. From our data we can exclude companions more massive than 10M_{jup}_ within the gap at a separation of ~230mas (~35au). Additional data are required to characterize the disk's peculiar morphology and to set tighter constraints on the potential perturber's orbital parameters and mass.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A73
- Title:
- Discovery of the directly imaged planet YSES 2b
- Short Name:
- J/A+A/648/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the origin and formation pathway of wide-orbit gas giant planets, it is necessary to expand the limited sample of these objects. The mass of exoplanets derived with spectrophotometry, however, varies strongly as a function of the age of the system and the mass of the primary star. By selecting stars with similar ages and masses, the Young Suns Exoplanet Survey (YSES) aims to detect and characterize planetary-mass companions to solar-type host stars in the Scorpius-Centaurus association. Our survey is carried out with VLT/SPHERE with short exposure sequences on the order of 5-min per star per filter. The subtraction of the stellar point spread function (PSF) is based on reference star differential imaging (RDI) using the other targets (with similar colors and magnitudes) in the survey in combination with principal component analysis. Two astrometric epochs that are separated by more than one year are used to confirm co-moving companions by proper motion analysis. We report the discovery of YSES 2b, a co-moving, planetary-mass companion to the K1 star YSES 2 (TYC 8984-2245-1, 2MASS J11275535-6626046). The primary has a Gaia EDR3 distance of 110pc, and we derive a revised mass of 1.1M_{sun}_ and an age of approximately 14Myr. We detect the companion in two observing epochs southwest of the star at a position angle of 205{deg} and with a separation of ~1.05", which translates to a minimum physical separation of 115au at the distance of the system. Photometric measurements in the H and Ks bands are indicative of a late L spectral type, similar to the innermost planets around HR 8799. We derive a photometric planet mass of 6.3^+1.6^_-0.9_M_{Jup}_ using AMES-COND and AMES-dusty evolutionary models; this mass corresponds to a mass ratio of q=(0.5+/-0.1)% with the primary. This is the lowest mass ratio of a direct imaging planet around a solar-type star to date. We discuss potential formation mechanisms and find that the current position of the planet is compatible with formation by disk gravitational instability, but its mass is lower than expected from numerical simulations. Formation via core accretion must have occurred closer to the star, yet we do not find evidence that supports the required outward migration, such as via scattering off another undiscovered companion in the system. We can exclude additional companions with masses greater than 13M_{Jup}_ in the full field of view of the detector (0.15"<{rho}<5.50"), at 0.5" we can rule out further objects that are more massive than 6M_{Jup}_, and for projected separations {rho}>2arcsec we are sensitive to planets with masses as low as 2M_{Jup}_. YSES 2b is an ideal target for follow-up observations to further the understanding of the physical and chemical formation mechanisms of wide-orbit Jovian planets. The YSES strategy of short snapshot observations (<=5min) and PSF subtraction based on a large reference library proves to be extremely efficient and should be considered for future direct imaging surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/773/135
- Title:
- Disk-bearing stars in Cygnus OB2
- Short Name:
- J/ApJ/773/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star-forming regions is hampered by their typically large distances to the Sun. One exception to this is the massive star-forming region Cygnus OB2 in the Cygnus X region, at the distance of ~1400pc. Cygnus OB2 hosts very rich populations of massive and low-mass stars, being the best target in our Galaxy to study the formation of stars, circumstellar disks, and planets in the presence of massive stars. In this paper, we combine a wide and deep set of photometric data, from the r band to 24{mu}m, in order to select the disk-bearing population of stars in Cygnus OB2 and identify the class I, class II, and stars with transition and pre-transition disks. We selected 1843 sources with infrared excesses in an area of 1{deg}x1{deg} centered on Cyg OB2 in several evolutionary stages: 8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition disks, and 3.3% transition disks. The spatial distribution of these sources shows a central cluster surrounded by an annular overdensity and some clumps of recent star formation in the outer region. Several candidate subclusters are identified, both along the overdensity and in the rest of the association.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A96
- Title:
- Disk-locking PMS evolutionary tracks
- Short Name:
- J/A+A/586/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotational evolution in young stars is described by pre-main sequence evolutionary tracks including non-gray boundary conditions, rotation, conservation of angular momentum, and simulations of disk-locking. By assuming that disk-locking is the regulation mechanism for the stellar angular velocity during the early stages of pre-main sequence evolution, we use our rotating models and observational data to constrain disk lifetimes (Tdisk) of a representative sample of low-mass stars in two young clusters, the Orion Nebula cluster (ONC) and NGC 2264, and to better understand their rotational evolution. The period distributions of the ONC and NGC 2264 are known to be bimodal and to depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated sets of evolutionary tracks from a fully convective configuration with low central temperatures (before D- and Li-burning). We assumed that the evolution of fast rotators can be represented by models considering conservation of angular momentum during all stages and of moderate rotators by models considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A85
- Title:
- Disk masses in the Orion Molecular Cloud-2
- Short Name:
- J/A+A/628/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass evolution of protoplanetary disks is driven by internal processes and by external factors such as photoevaporation. Disentangling these two effects, however, remains difficult. We measured the dust masses of a sample of 132 disks in the Orion Molecular Cloud 2 (OMC-2) region, and compared them to externally photoevaporated disks in the Trapezium cluster, and to disks in nearby low-mass star-forming regions (SFRs). This allowed us to test whether initial disk properties are the same in high- and low-mass SFRs, and enabled a direct measurement of the effect of external photoevaporation on disks. A ~20'x4'mosaic of 3mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) was used to measure the fluxes of 132 disks and 35 protostars >0.5pc away from the Trapezium. We identify and characterize a sample of 34 point sources not included in the Spitzer catalog on which the sample is based. Of the disks, 37 (28%) are detected, and have masses ranging from 7-270M_{sun}_. The detection rate for protostars is higher (69%). Disks near the Trapezium are found to be less massive by a factor 0.18^+0.18^_-0.11), implying a mass loss rate of 8x10^-8^M_{sun}_/yr. Our observations allow us to distinguish the impact of time and environment on disk evolution in a single SFR. The disk mass distribution in OMC-2 is statistically indistinguishable from that in nearby low-mass SFRs like Lupus and Taurus. We conclude that age is the main factor that determines the evolution of these disks. This result is robust with respect to assumptions of dust temperature, sample incompleteness, and biases. The difference between the OMC-2 and Trapezium cluster samples is consistent with mass loss driven by far-ultraviolet radiation near the Trapezium. Taken together, this implies that in isolation disk formation and evolution proceed similarly, regardless of cloud mass.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/362
- Title:
- Disks around brown dwarfs in {sigma} Ori cluster
- Short Name:
- J/ApJ/688/362
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a census of circumstellar disks around brown dwarfs in the {sigma} Ori cluster using all available images from the Infrared Array Camera on board the Spitzer Space Telescope. To search for new low-mass cluster members with disks, we have measured photometry for all sources in the Spitzer images and have identified the ones that have red colors that are indicative of disks. We present five promising candidates, which may consist of two brown dwarfs, two stars with edge-on disks, and a low-mass protostar if they are bona fide members. Spectroscopy is needed to verify the nature of these sources. We have also used the Spitzer data to determine which of the previously known probable members of {sigma} Ori are likely to have disks. By doing so, we measure disk fractions of ~40% and ~60% for low-mass stars and brown dwarfs, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A82
- Title:
- Disks around T Tauri stars with SPHERE. II.
- Short Name:
- J/A+A/633/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-IR polarimetric images of protoplanetary disks provide the ability to characterize sub-structures that are potentially due to the interaction with (forming) planets. The available census is, however, strongly biased toward massive disks around old stars. The DARTTS program aims at alleviating this bias by imaging a large number of T Tauri stars with diverse properties. DARTTS-S employs VLT/SPHERE to image the polarized scattered light from disks. In parallel, DARTTS-A is providing ALMA images of the same targets for a comparison of different dust components. In this work, we present new SPHERE images of 21 circumstellar disks, which is the largest sample of this time yet to be released. A re-calculation of some relevant stellar and disk properties following Gaia DR2 is also performed. The targets of this work are significantly younger than those published thus far with polarimetric NIR imaging. Scattered light is unambiguously resolved in 11 targets while some polarized unresolved signal is detected in 3 additional sources. Some disk sub-structures are detected. However, the paucity of spirals and shadows from this sample reinforces the trend for which these NIR features are associated with Herbig stars, either because older or more massive. Furthermore, disk rings that are apparent in ALMA observations of some targets do not appear to have corresponding detections with SPHERE. Inner cavities larger than 15au are also absent from our images despite being expected from the SED. On the other hand, 3 objects show extended filaments at larger scale that are indicative of strong interaction with the surrounding medium. All but one of the undetected disks are best explained by their limited size (<~20au) and the high occurrence of stellar companions in these sources suggest an important role in limiting the disk size. One undetected disk is massive and very large at millimeter wavelengths implying it is self-shadowed in the near-IR. This work paves the way towards a more complete and less biased sample of scattered-light observations, which is required to interpret how disk features evolve throughout the disk lifetime.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A99
- Title:
- DoAr 44 ugri light curves
- Short Name:
- J/A+A/643/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young stars interact with their accretion disk through their strong magnetosphere. We aim to investigate the magnetospheric accretion/ejection process in the young stellar system DoAr 44 (V2062 Oph). We monitored the system over several rotational cycles, combining high-resolution spectropolarimetry at both optical and near-IR wavelengths with long-baseline near-IR inteferometry and multicolor photometry. We derive a rotational period of 2.96d from the system's light curve, which is dominated by stellar spots. We fully characterize the central star's properties from the high signal-to-noise, high-resolution optical spectra we obtained during the campaign. DoAr 44 is a young 1.2M_{sun}_ star, moderately accreting from its disk (Macc=6.510^-9^M_{sun}_/yr), and seen at a low inclination (i~=30{deg}). Several optical and near-IR line profiles probing the accretion funnel flows (H{alpha}, H{beta}, HeI 1083nm, Pa{beta}) and the accretion shock (HeI 587.6nm) are modulated at the stellar rotation period. The most variable line profile is HeI 1083nm, which exhibits modulated redshifted wings that are a signature of accretion funnel flows, as well as deep blueshifted absorptions indicative of transient outflows. The Zeeman-Doppler analysis suggests the star hosts a mainly dipolar magnetic field, inclined by about 20{deg} onto the spin axis, with an intensity reaching about 800G at the photosphere, and up to 2+/-0.8kG close to the accretion shock. The magnetic field appears strong enough to disrupt the inner disk close to the corotation radius, at a distance of about 4.6R* (0.043au), which is consistent with the 5R* (0.047au) upper limit we derived for the size of the magnetosphere in our Paper I from long baseline interferometry. DoAr 44 is a pre-transitional disk system, exhibiting a 25-30au gap in its circumstellar disk, with the inner and outer disks being misaligned. On a scale of 0.1au or less, our results indicate that the system is steadily accreting from its inner disk through its tilted dipolar magnetosphere. We conclude that in spite of a highly structured disk on the large scale, perhaps the signature of ongoing planetary formation, the magnetospheric accretion process proceeds unimpeded at the star-disk interaction level.
