- ID:
- ivo://CDS.VizieR/J/MNRAS/461/1734
- Title:
- HAWK-I JHK photometry of the Orion Nebula Cloud
- Short Name:
- J/MNRAS/461/1734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Due to its youth, proximity and richness, the Orion nebula cloud (ONC) is an ideal testbed to obtain a comprehensive view on the initial mass function (IMF) down to the planetary mass regime. Using the HAWK-I camera at the VLT, we have obtained an unprecedented deep and wide near-infrared JHK mosaic of the ONC (90 per cent completeness at K ~19.0mag, 22x28 arcmin^2^). Applying the most recent isochrones and accounting for the contamination of background stars and galaxies, we find that ONC's IMF is bimodal with distinct peaks at about 0.25 and 0.025M_{sun}_ separated by a pronounced dip at the hydrogen burning limit (0.08M_{sun}_), with a depth of about a factor of 2-3 below the log-normal distribution. Apart from ~920 low-mass stars (M<1.4M_{sun}_) the IMF contains ~760 brown dwarf candidates and ~160 isolated planetary mass object candidates with M>0.005M_{sun}_, hence about 10 times more substellar candidates than known before. The substellar IMF peak at 0.025M_{sun}_ could be caused by brown dwarfs and isolated planetary mass objects which have been ejected from multiple systems during the early star formation process or from circumstellar discs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/129/856
- Title:
- Herbig Ae/Be stars in nearby OB associations
- Short Name:
- J/AJ/129/856
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a study of the early-type stars in nearby OB associations spanning an age range of ~3-16Myr, with the aim of determining the fraction of stars that belong to the Herbig Ae/Be class. We studied the B, A, and F stars in the nearby (<=500pc) OB associations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1, with membership determined from Hipparcos (Cat. <I/239>) data. We also included in our study the early-type stars in the Trumpler 37 cluster, part of the Cep OB2 association. We obtained spectra for 440 Hipparcos stars in these associations, from which we determined accurate spectral types, visual extinctions, effective temperatures, luminosities and masses, using Hipparcos photometry.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/100
- Title:
- Herschel FIR observations of NGC3603
- Short Name:
- J/ApJ/799/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed the giant H II region around the NGC 3603 young stellar cluster (YC) with the five broad bands (70, 160, 250, 350, 500{mu}m) of the SPIRE and PACS instruments, on board the Herschel Space Observatory. Together with what is currently known of the stellar, atomic, molecular, and warm dust components, this additional and crucial information should allow us to better understand the details of the star-formation history in this region. The main objective of the investigation is to study, at high spatial resolution, the distribution and main physical characteristics of the cold dust. By reconstructing the temperature and density maps, we found, respectively, a mean value of 36K and log_10_N_H_=22.0+/-0.1/cm2. We carried out a photometric analysis detecting 107 point-like sources, mostly confined to the north and south of the cluster. By comparing our data with spectral energy distribution models, we found that 35 sources are well represented by young stellar objects in early evolutionary phases, from Class 0 to Class I. The Herschel detections also provided far-IR counterparts for 4 H_2_O masers and 11 objects previously known from mid-IR observations. The existence of so many embedded sources confirms the hypothesis of intense and ongoing star-formation activity in the region around NGC 3603 YC.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/1760
- Title:
- Hierarchical formation of Westerlund 1
- Short Name:
- J/MNRAS/472/1760
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the level of substructure and mass segregation in the massive, young cluster Westerlund 1. We find that it is relatively smooth, with little or no mass segregation, but with the massive stars in regions of significantly higher than average surface density. While an expanding or bouncing-back scenario for the evolution of Westerlund 1 cannot be ruled out, we argue that the most natural model to explain these observations is one in which Westerlund 1 formed with no primordial mass segregation and at a similar or larger size than we now observe.
- ID:
- ivo://CDS.VizieR/J/A+A/501/563
- Title:
- HKs photometry in the Arches cluster
- Short Name:
- J/A+A/501/563
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The massive Arches cluster near the Galactic center should be an ideal laboratory for investigating massive star formation under extreme conditions. But it comes at a high price: the cluster is hidden behind several tens of magnitudes of visual extinction. Severe crowding requires space or AO-assisted instruments to resolve the stellar populations, and even with the best instruments interpreting the data is far from direct. Several investigations using NICMOS and the most advanced AO imagers on the ground revealed an overall top-heavy IMF for the cluster, with a very flat IMF near the center. There are several effects, however, that could potentially bias these results, in particular the strong differential extinction and the problem of transforming the observations into a standard photometric system in the presence of strong reddening. We present new observations obtained with the NAOS-Conica (NACO) AO-imager on the VLT. The problem of photometric transformation is avoided by working in the natural photometric system of NACO, and we use a Bayesian approach to determine masses and reddenings from the broad-band IR colors. A global value of Gamma=-1.1+/-0.2 for the high-mass end (M>10M_{sun}_) of the IMF is obtained, and we conclude that a power law of Salpeter slope cannot be discarded for the Arches cluster. The flattening of the IMF towards the center is confirmed, but is less severe than previously thought. We find Gamma=-0.88+/-0.20, which is incompatible with previous determinations. Within 0.4pc we derive a total mass of ~2.0(+/-0.6)x10^4^M_{sun}_ for the cluster and a central mass density rho=2(+/-0.4)x10^5^M_{sun}_/pc^3^ that confirms Arches as the densest known young massive cluster in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/other/NewA/58.1
- Title:
- Hogg 16 peculiar stars
- Short Name:
- J/other/NewA/58.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of chemically peculiar (CP) stars in open clusters provides valuable information about their evolutionary status. Their detection can be performed using the Delta-a photometric system, which maps a characteristic flux depression at lambda 5200{AA}. This paper aims at studying the occurrence of CP stars in the earliest stages of evolution of a stellar population by applying this technique to Hogg 16, a very young Galactic open cluster (about 25Myr). We identified several peculiar candidates: two B-type stars with a negative Delta-a index (CD-60 4701, CPD-60 4706) are likely emission-line (Be) stars, even though spectral measurements are necessary for a proper classification of the second one; a third object (CD-60 4703), identified as a Be candidate in literature, appears to be a background B-type supergiant with no significant Delta-a index, which does not rule out the possibility that it is indeed peculiar as the normality line of Delta-a for supergiants has not been studied in detail yet. A fourth object (CD-60 4699) appears to be a magnetic CP star of 8 Msun, but obtained spectral data seem to rule out this hypothesis. Three more magnetic CP star candidates are found in the domain of early F-type stars. One is a probable nonmember and close to the border of significance, but the other two are probably pre-main sequence cluster objects. This is very promising, as it can lead to very strong constraints to the diffusion theory. Finally, we derived the fundamental parameters of Hogg 16 and provide for the first time an estimate of its metal content.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/72.257
- Title:
- Homogeneous Catalog of Open Cluster Param.
- Short Name:
- J/other/AstBu/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the current version of the "Homogeneous Catalog of Open Clusters Parameters", supported by our group during last decades. The catalog is created on the base of redetermination of the main parameters of clusters (colour excesses, distances from the Sun and ages) using published photometric measurements, in particular, according to the 2MASS catalog of point sources. At present, the catalog contains parameters of 1035 clusters. The catalog includes the radial velocities data for 496 open clusters. All clusters of the catalog have estimates of the components of proper motion.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A13
- Title:
- Homogeneous sample of F6-K4 Hyades stars
- Short Name:
- J/A+A/547/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar kinematic groups are kinematical coherent groups of stars that might have a common origin. These groups are dispersed throughout the Galaxy over time by the tidal effects of both Galactic rotation and disc heating, although their chemical content remains unchanged. The aim of chemical tagging is to establish that the abundances of every element in the analysis are homogeneous among the members. We study the case of the Hyades Supercluster to compile a reliable list of members (FGK stars) based on our chemical tagging analysis. For a total of 61 stars from the Hyades Supercluster, stellar atmospheric parameters (Teff, logg, {ksi}, and [Fe/H]) are determined using our code called StePar, which is based on the sensitivity to the stellar atmospherics parameters of the iron EWs measured in the spectra. We derive the chemical abundances of 20 elements and find that their [X/Fe] ratios are consistent with Galactic abundance trends reported in previous studies. The chemical tagging method is applied with a carefully developed differential abundance analysis of each candidate member of the Hyades Supercluster, using a well-known member of the Hyades cluster as a reference (vB 153). We find that only 28 stars (26 dwarfs and 2 giants) are members, i.e. that 46% of our candidates are members based on the differential abundance analysis. This result confirms that the Hyades Supercluster cannot originate solely from the Hyades cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/355/651
- Title:
- HRI observations of PMS stars in NGC 2264
- Short Name:
- J/A+A/355/651
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze six ROSAT HRI observations pointed toward the Star Forming Region (SFR) NGC 2264. Three are pointed to the southern star formation core, the other three about 20' to the north. We detect 169 X-ray sources, ~95% of which are likely to be Pre Main Sequence (PMS) stars, significantly enlarging the known population of the SFR in the area covered by the observations. Using published BVRI photometry we place the X-ray sources with well defined optical counterparts on the HRI diagram and estimate their masses and ages. Our comparison of the mass function and age distribution of the X-ray sources with results previously obtained for NGC 2264, demonstrates that deep X-ray observations provide, at least in this case, a very efficient method of selecting SFR members and does not introduce stronger biases than other methods.
- ID:
- ivo://CDS.VizieR/J/ApJS/166/549
- Title:
- HST/ACS observations of NGC 346
- Short Name:
- J/ApJS/166/549
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric study of the star-forming region NGC 346 and its surrounding field in the Small Magellanic Cloud, using data taken with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). The data set contains both short and long exposures for increased dynamic range, and photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected almost 100,000 stars over a magnitude range of V~11 to V~28 mag, including all stellar types from the most massive young stars to faint lower main-sequence and pre-main-sequence stars. We find that this region, which is characterized by a plethora of stellar systems and interesting objects, is an outstanding example of mixed stellar populations. We take into account different features of the color-magnitude diagram of all the detected stars to distinguish the two dominant stellar systems: the stellar association NGC 346 and the old spherical star cluster BS 90. These observations provide a complete stellar sample of a field about 5'x5' around the most active star-forming region in this galaxy. Considering the importance of these data for various investigations in the area, we provide the full stellar catalog from our photometry. This paper is the first part of an ongoing study to investigate in detail the two dominant stellar systems in the area and their surrounding field.
