Context.
Debris discs orbiting young stars are key to understanding dust evolution and the planetary formation process. We take advantage of a recent membership analysis of the 30 Myr nearby open ...cluster IC 4665 based on the
Gaia
and DANCe surveys to revisit the disc population of this cluster.
Aims.
We aim to study the disc population of IC 4665 using
Spitzer
(MIPS and IRAC) and WISE photometry.
Methods.
We use several colour–colour diagrams with empirical photospheric sequences to detect the sources with an infrared excess. Independently, we also fit the spectral energy distribution (SED) of our debris-disc candidates with the Virtual Observatory SED analyser (VOSA) which is capable of automatically detecting infrared excesses and provides effective temperature estimates.
Results.
We find six candidate debris-disc host stars (five with MIPS and one with WISE), two of which are new candidates. We estimate a disc fraction of 24 ± 10% for the B–A stars, where our sample is expected to be complete. This is similar to what has been reported in other clusters of similar ages (Upper Centaurus Lupus, Lower Centaurus Crux, the
β
Pictoris moving group, and the Pleiades). For solar-type stars we find a disc fraction of 9 ± 9%, which is lower than that observed in regions with comparable ages.
Conclusions.
Our candidate debris-disc host stars are excellent targets to be studied with ALMA or the future
James Webb
Space Telescope (JWST).
Context.
As a fragile element, lithium is a sensitive probe of physical processes occurring in stellar interiors.
Aims.
We aim to investigate the relationship between lithium abundance and rotation ...rate in low-mass members of the newly discovered 125 Myr-old Psc–Eri stellar stream.
Methods.
We obtained high-resolution optical spectra and measured the equivalent width of the 607.8 nm LiI line for 40 members of the Psc–Eri stream, whose rotational periods have been previously derived.
Results.
We show that a tight correlation exists between the lithium content and rotation rate among the late-G to early-K-type stars of the Psc–Eri stream. Fast rotators are systematically Li rich, while slow rotators are Li depleted. This trend mimics that previously reported for the similar age Pleiades cluster.
Conclusions.
The lithium-rotation connection thus seems to be universal over a restricted effective temperature range for low-mass stars at or close to the zero-age main sequence, and does not depend on environmental conditions.
Orion revisited Bouy, H; Alves, J; Bertin, E ...
Astronomy and astrophysics (Berlin),
04/2014, Letnik:
564
Journal Article
Recenzirano
Odprti dostop
Aims. Following the recent discovery of a large population of young stars in front of the Orion nebula, we carried out an observational campaign with the DECam wide-field camera covering ...approximately 10 deg super(2) centered on NGC 1980 to confirm, probe the extent of, and characterize this foreground population of pre-main-sequence stars. Methods. We used multiwavelength wide-field images and catalogs to identify potential foreground pre-main-sequence stars using a novel probabilistic technique based on a careful selection of colors and luminosities. Results. We confirm the presence of a large foreground population towards the Orion A cloud. This population contains several distinct subgroups, including NGC 1980 and NGC 1981, and stretches across several degrees in front of the Orion A cloud. By comparing the location of their sequence in various color-magnitude diagrams with other clusters, we found a distance and an age of 380 pc and 5 similar to 10 Myr, in good agreement with previous estimates. Our final sample includes 2123 candidate members and is complete from below the hydrogen-burning limit to about 0.3 M sub(middot in circle), where the data start to be limited by saturation. Extrapolating the mass function to the high masses, we estimate a total number of approximately 2600 members in the surveyed region. Conclusions. We confirm the presence of a rich, contiguous, and essentially coeval population of about 2600 foreground stars in front of the Orion A cloud, loosely clustered around NGC 1980, NGC 1981, and a new group in the foreground of the OMC-2/3. For the area of the cloud surveyed, this result implies that there are more young stars in the foreground population than young stars inside the cloud. Assuming a normal initial mass function, we estimate that between one to a few supernovae must have exploded in the foreground population in the past few million years, close to the surface of Orion A, which might be responsible, together with stellar winds, for the structure and star formation activity in these clouds. This long-overlooked foreground stellar population is of great significance, calling for a revision of the star formation history in this region of the Galaxy.
ABSTRACT We use K2 to continue the exploration of the distribution of rotation periods in Pleiades that we began in Paper I. We have discovered complicated multiperiod behavior in Pleiades stars ...using these K2 data, and we have grouped them into categories, which are the focal part of this paper. About 24% of the sample has multiple, real frequencies in the periodogram, sometimes manifesting as obvious beating in the LCs. Those having complex and/or structured periodogram peaks, unresolved multiple periods, and resolved close multiple periods are likely due to spot/spot group evolution and/or latitudinal differential rotation; these largely compose the slowly rotating sequence in P versus (V − Ks)0 identified in Paper I. The fast sequence in P versus (V − Ks)0 is dominated by single-period stars; these are likely to be rotating as solid bodies. Paper III continues the discussion, speculating about the origin and evolution of the period distribution in the Pleiades.
Context. Lithium (Li) abundance is an age indicator for G, K, and M stellar types, as its abundance decreases over time for these spectral types. However, despite all of the observational efforts ...made over the past few decades, the role of rotation, stellar activity, and metallicity in the depletion of Li is still unclear. Aims. Our purpose is to investigate how Li depletion is affected by rotation and metallicity in G and K members of the roughly Pleiades-aged open cluster M35. Methods. We have collected an initial sample of 165 candidate members observed with the WIYN/Hydra spectrograph. In addition, we have taken advantage of three previous spectroscopic studies of Li in M35. As a result, we have collected a final sample of 396 stars observed with the same instrument, which we have classified as non-members, possible non-members, possible members, and probable members of the cluster. We have measured iron abundances, Li equivalent widths, and Li abundances for the 110 M35 members added to the existing sample by this study. Finally, rotation periods for cluster members have been obtained from the literature or derived from Zwicky Transient Facility light curves. Results. We have confirmed that fast G and K rotators are Li-rich in comparison with slow rotators of similar effective temperature. This trend, which is also seen in previous studies, is more evident when binaries are not taken into account. Furthermore, while we derived an average metallicity of Fe/H = −0.26 ± 0.09 from our spectra, the distribution of Li in M35 is similar to those observed for the Pleiades and M34 open clusters, which have solar metallicity and slightly different ages. In addition, we have shown that an empirical relationship proposed to remove the contribution of the Fe I line at 670.75 nm to the blended feature at 670.78 nm overestimates by 5–15 mÅ the contribution of this iron line for M35 members. Conclusions. M35 fast G and K rotators have depleted less Li than their slower counterparts. Furthermore, a 0.2−0.3 dex difference in metallicity appears to make little difference in the Li distributions of open clusters with ages between 100 and 250 Myr.
The evolution of planetary systems is intimately linked to the evolution of their host stars. Although several theories have been proposed, the question of how planets die remains open owing to the ...small number statistics, making it clear that the sample of planets around post-main sequence stars needs to be enlarged. In this work we study the giant star Kepler-91 (KOI-2133) in order to determine the nature of a transiting companion. However, its planetary confirmation is needed due to the large pixel size of the Kepler camera, which can hide other stellar configurations able to mimic planet-like transit events. Kepler-91b could be the previous stage of the planet engulfment, which has recently been detected for BD+48 740. Our estimations show that Kepler-91b will be swallowed by its host star in less than 55 Myr. At pericentre, the star subtends an angle of 48degrees, covering around 10% of the sky as seen from the planet. The planetary atmosphere seems to be inflated probably due to the high stellar irradiation.
Context. Brown dwarfs represent a sizable fraction of the stellar content of our Galaxy and populate the transition between the stellar and planetary mass regime. There is, however, no agreement on ...the processes responsible for their formation. Aims. We have conducted a large survey of the young, nearby cluster IC 348, to uncover its low-mass brown dwarf population and have studied the cluster properties in the substellar regime. Methods. Deep optical and near-IR images taken with MegaCam and WIRCam at the Canada-France-Hawaii Telescope (CFHT) were used to select photometric candidate members. A spectroscopic follow-up of a large fraction of the candidates was conducted to assess their youth and membership. Results. We confirmed spectroscopically 16 new members of the IC 348 cluster, including 13 brown dwarfs, contributing significantly to the substellar census of the cluster, where only 30 brown dwarfs were previously known. Five of the new members have a L0 spectral type, the latest-type objects found to date in this cluster. At 3 Myr, evolutionary models estimate these brown dwarfs to have a mass of ~13 MJup. Combining the new members with previous census of the cluster, we constructed the initial mass function (IMF) complete down to 13 MJup. Conclusions. The IMF of IC 348 is well fitted by a log-normal function and we do not see evidence for variations of the mass function down to planetary masses when compared to other young clusters.
We present a comprehensive study of star-forming (SF) galaxies in the Hubble Space Telescope
(HST) Frontier Field recent cluster merger A2744 (z = 0.308). Wide-field, ultraviolet–infrared (UV–IR) ...imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFRUV+IR = 343 ± 10 M⊙ yr−1. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFRUV+IR = 201 ± 9 M⊙ yr−1. Focusing on obscured star formation, this core region exhibits a total SFRIR = 138 ± 8 M⊙ yr−1, a mass-normalized SFRIR of ΣSFR = 11.2 ± 0.7 M⊙ yr−1 per 1014 M⊙ and a fraction of IR-detected SF galaxies
$f_{\rm SF} = 0.080^{+0.010}_{-0.037}$
. Overall, the cluster population at z ∼ 0.3 exhibits significant intrinsic scatter in IR properties (total SFRIR, T
dust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galaxies with substantial unobscured SF due to extreme stripping (SFRUV/SFRIR up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.
The Seven Sisters DANCe Bouy, H; Berlin, E; Sarro, L M ...
Astronomy and astrophysics (Berlin),
05/2015, Letnik:
577
Journal Article
Recenzirano
Odprti dostop
Context. The DANCe survey provides photometric and astrometric (position and proper motion) measurements for approximately 2 million unique sources in a region encompassing ~80 deg super(2) centered ...on the Pleiades cluster. Aims. We aim at deriving a complete census of the Pleiades and measure the mass and luminosity functions of the cluster. Methods. Using the probabilistic selection method previously described, we identified high probability members in the DANCe (i > or = 14 mag) and Tycho-2 (V <, ~ 12 mag) catalogues and studied the properties of the cluster over the corresponding luminosity range. Results. We find a total of 2109 high-probability members, of which 812 are new, making it the most extensive and complete census of the cluster to date. The luminosity and mass functions of the cluster are computed from the most massive members down to ~0.025 M sub(middot in circle). The size, sensitivity, and quality of the sample result in the most precise luminosity and mass functions observed to date for a cluster. Conclusions. Our census supersedes previous studies of the Pleiades cluster populations, in terms of both sensitivity and accuracy.
Context.
The analysis of luminosity and mass distributions of young stellar clusters is essential to understanding the star-formation process. However, the gas and dust left over by this process ...extinct the light of the newborn stars and can severely bias both the census of cluster members and itsss luminosity distribution.
Aims.
We aim to develop a Bayesian methodology to infer, with minimal biases due to photometric extinction, the candidate members and magnitude distributions of embedded young stellar clusters.
Methods.
We improve a previously published methodology and extend its application to embedded stellar clusters. We validate the method using synthetically extincted data sets of the Pleiades cluster with varying degrees of extinction.
Results.
Our methodology can recover members from data sets extincted up to
A
v
∼ 6 mag with accuracies, true positive, and contamination rates that are better than 99%, 80%, and 9%, respectively. Missing values hamper our methodology by introducing contaminants and artifacts into the magnitude distributions. Nonetheless, these artifacts vanish through the use of informative priors in the distribution of the proper motions.
Conclusions.
The methodology presented here recovers, with minimal biases, the members and distributions of embedded stellar clusters from data sets with a high percentage of sources with missing values (> 96%).
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