- ID:
- ivo://CDS.VizieR/J/MNRAS/458/3027
- Title:
- Young and embedded clusters in Cygnus-X
- Short Name:
- J/MNRAS/458/3027
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide a new view on the Cygnus-X north complex by accessing for the first time the low mass content of young stellar populations in the region. CFHT/WIRCam camera was used to perform a deep near-IR survey of this complex, sampling stellar masses down to ~0.1M_{sun}_. Several analysis tools, including a extinction treatment developed in this work, were employed to identify and uniformly characterise a dozen unstudied young star clusters in the area. Investigation of their mass distributions in low-mass domain revealed a relatively uniform log-normal IMF with a characteristic mass of 0.32+/-0.08M_{sun}_ and mass dispersion of 0.40+/-0.06. In the high mass regime, their derived slopes showed that while the youngest clusters (age<4Myr) presented slightly shallower values with respect to the Salpeter's, our older clusters (4Myr<age<18Myr) showed IMF compliant values and a slightly denser stellar population. Although possibly evidencing a deviation from an 'universal' IMF, these results also supports a scenario where these gas dominated young clusters gradually 'build up' their IMF by accreting low-mass stars formed in their vicinity during their first ~3Myr, before the gas expulsion phase, emerging at the age of ~4Myr with a fully fledged IMF. Finally, the derived distances to these clusters confirmed the existence of at least 3 different star forming regions throughout Cygnus-X north complex, at distances of 500-900pc, 1.4-1.7kpc and 3.0kpc, and revealed evidence of a possible interaction between some of these stellar populations and the Cygnus-OB2 association.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/155/109
- Title:
- Young binaries in Ophiuchus&Upper Centaurus-Lupus
- Short Name:
- J/AJ/155/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of the orbital positions and flux ratios of 17 binary and triple systems in the Ophiuchus star-forming region and the Upper Centaurus-Lupus cluster based on adaptive optics imaging at the Keck Observatory. We report the detection of visual companions in MML 50 and MML 53 for the first time, as well as the possible detection of a third component in WSB 21. For six systems in our sample, our measurements provide a second orbital position following their initial discoveries over a decade ago. For eight systems with sufficient orbital coverage, we analyze the range of orbital solutions that fit the data. Ultimately, these observations will help provide the groundwork toward measuring precise masses for these pre-main-sequence stars and understanding the distribution of orbital parameters in young multiple systems.
- ID:
- ivo://CDS.VizieR/J/A+A/480/735
- Title:
- Young local stellar associations
- Short Name:
- J/A+A/480/735
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ~100pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations - including an important fraction whose members are Hipparcos stars - offer insights into the star formation process in low-density environments, shed light on the substellar domain, and could have played an important role in the recent history of the local interstellar medium. To study the kinematic evolution of young local associations and their relation to other young stellar groups and structures in the local interstellar medium, thus casting new light on recent star formation processes in the solar neighbourhood.
- ID:
- ivo://CDS.VizieR/J/A+AS/139/393
- Title:
- Young Massive Star Clusters. II.
- Short Name:
- J/A+AS/139/393
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 4 lists photometric data for Young Massive Star Clusters identified in a sample of 21 nearby galaxies. The photometric data have been corrected for Galactic foreground extinction. Each cluster is identified by the abbreviated NGC number of its host galaxy and an object number: nxxx-yyy is object number yyy in the galaxy NGC xxx. Effective cluster radii have been obtained by modeling the cluster images as MOFFAT15 functions convolved with the point-spread function measured on the CCD images.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/92
- Title:
- Young massive star clusters in 2 LEGUS galaxies
- Short Name:
- J/ApJ/841/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the effective (half-light) radii and other structural properties of a systematically selected sample of young, massive star clusters (>=5x10^3^M_{sun}_ and <=200Myr) in two nearby spiral galaxies, NGC 628 and NGC 1313. We use Hubble Space Telescope (HST) WFC3/UVIS and archival ACS/WFC data obtained by the Legacy Extragalactic UV Survey (LEGUS), an HST Treasury Program. We measure effective radii with GALFIT, a two- dimensional image-fitting package, and with a new technique to estimate effective radii from the concentration index of observed clusters. The distribution of effective radii from both techniques spans ~0.5-10pc and peaks at 2-3pc for both galaxies. We find slight positive correlations between effective radius and cluster age in both galaxies, but no significant relationship between effective radius and galactocentric distance. Clusters in NGC 1313 display a mild increase in effective radius with cluster mass, but the trend disappears when the sample is divided into age bins. We show that the vast majority of the clusters in both galaxies are much older than their dynamical times, suggesting they are gravitationally bound objects. We find that about half of the clusters in NGC 628 are underfilling their Roche lobes, based on their Jacobi radii. Our results suggest that the young, massive clusters in NGC 628 and NGC 1313 are expanding, due to stellar mass loss or two-body relaxation, and are not significantly influenced by the tidal fields of their host galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/593
- Title:
- Young moving groups in solar neighbourhood
- Short Name:
- J/MNRAS/454/593
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a self-consistent, absolute isochronal age scale for young (<~200Myr), nearby (<~100pc) moving groups in the solar neighbourhood based on homogeneous fitting of semi-empirical pre-main-sequence model isochrones using the {tau}^2^ maximum-likelihood fitting statistic of Naylor & Jeffries (2006MNRAS.373.1251N) in the M_V_, V-J colour-magnitude diagram. The final adopted ages for the groups are as follows: 149^+51^_-19_Myr for the AB Dor moving group, 24+/-3Myr for the {beta} Pic moving group (BPMG), 45^+11^_-7_Myr for the Carina association, 42^+6^_-4_Myr for the Columba association, 11+/-3Myr for the {eta} Cha cluster, 45+/-4Myr for the Tucana-Horologium moving group (Tuc-Hor), 10+/-3Myr for the TW Hya association and 22^+4^_-3_Myr for the 32 Ori group. At this stage we are uncomfortable assigning a final, unambiguous age to the Argus association as our membership list for the association appears to suffer from a high level of contamination, and therefore it remains unclear whether these stars represent a single population of coeval stars. Our isochronal ages for both the BPMG and Tuc-Hor are consistent with recent lithium depletion boundary (LDB) ages, which unlike isochronal ages, are relatively insensitive to the choice of low-mass evolutionary models. This consistency between the isochronal and LDB ages instils confidence that our self-consistent, absolute age scale for young, nearby moving groups is robust, and hence we suggest that these ages be adopted for future studies of these groups. Software implementing the methods described in this study is available from http://www.astro.ex.ac.uk/people/timn/tau-squared/.
- ID:
- ivo://CDS.VizieR/J/ApJ/559/851
- Title:
- Young star cluster candidates in M31
- Short Name:
- J/ApJ/559/851
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of 60arcmin^2^, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (<~5pc), young (~10-200Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalog of the candidates including rough approximations of their reddenings and ages. We also look for patterns of cluster formation with galactocentric distance, but our rough estimates are not precise enough to reveal any clear patterns.
- ID:
- ivo://CDS.VizieR/J/AJ/109/960
- Title:
- Young star clusters in The Antennae
- Short Name:
- J/AJ/109/960
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New high-resolution images of the disks of NGC 4038/4039 obtained with the Wide Field Camera of the Hubble Space Telescope (HST) are presented. NGC 4038/4039, nicknamed "The Antennae," is a prototypical example of a pair of colliding galaxies believed to be at an early stage of a merger. Down to the limiting magnitude of V~23mag, the HST images reveal a population of over 700 blue pointlike objects within the disks. The mean absolute magnitude of these objects is M_V_=-11mag, with the brightest objects reaching M_V_~-15. Their mean apparent color indices are U-V=-0.7mag and V-I=0.8mag on the Johnson UVI passband system, while their mean indices corrected for internal reddening are (U-V)_0_=-1.0mag and (V-I)_0_=0.5. Their mean effective radius, determined from slightly resolved images, is 18pc (for H0=50km/s/Mpc). Based on their luminosities and resolution, most of these objects cannot be individual stars, but are likely young compact star clusters. The brighter ones are similar to the objects found in NGC 1275 and NGC 7252, which appear to be young globular clusters formed during recent galaxy mergers. Based on their U-V and V-I colors, the brightest, bluest clusters of NGC 4038/4039 appear to be less than 10Myr old. Most of these bright clusters are relatively tightly clustered themselves, with typically a dozen individual clusters belonging to a complex identified as a giant H II region from ground-based observations. The cluster luminosity function (LF) is approximately a power law, {Phi}(L)dL is proportional to L^(-1.78+/-0.05)^dL, with no hint of a turnover at fainter magnitudes. This power-law shape agrees with the LF of Magellanic Cloud clusters and Galactic open clusters, but differs from the LF of old globular cluster systems that is typically Gaussian with a FWHM of ~3mag. Possible explanations for this apparent difference include: (1) We have not observed faint enough to see the turnover, (2) the initial LF of star clusters is a power law but the fainter objects dissolve with time, (3) conditions at the present epoch favor the formation of a wide range of cluster masses while conditions at earlier epochs favored the formation of massive clusters, and (4) the NGC 4038/4039 clusters may not evolve into normal globular clusters. Besides the blue clusters, we also find about a dozen extremely red objects with V-I>3.0. The highest number density of these red objects is found in the SE quadrant, where star formation appears to be most recent. We propose that these objects may be very young star clusters still embedded in their placental dust cocoons.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A34
- Title:
- Young star groups in NGC 300
- Short Name:
- J/A+A/594/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study their hierarchical organization. The proximity and orientation of this Sculptor Group galaxy make it an ideal candidate for this study. The research was conducted using archival point spread function (PSF) fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). Using the path linkage criterion (PLC), we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. This method provided an additional tool for the detection of young stellar structures. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color (blue and red). A statistical decontamination of field stars was performed for each region. In this way it was possible to build the color-magnitude diagrams (CMD) and compare them with theoretical evolutionary models. We also constrained the present-day mass function (PDMF) per group by estimating a value for its slope. The blue population distribution in NGC 300 clearly follows the spiral arms of the galaxy, showing a hierarchical behavior in which the larger and loosely distributed structures split into more compact and denser ones over several density levels. We created a catalog of 1147 young star groups in six fields of the galaxy NGC 300, in which we present their fundamental characteristics. The mean and the mode radius values obtained from the size distribution are both 25pc, in agreement with the value for the Local Group and nearby galaxies. Additionally, we found an average PDMF slope that is compatible with the Salpeter value.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/545
- Title:
- Young stars in Cepheus OB3b
- Short Name:
- J/MNRAS/403/545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on time-scales of less than a day, to more than 20d. After rejection of contaminating objects using V, I, R and narrow-band H{alpha} photometry, we find 475 objects with measured rotation periods, which are very likely pre-main-sequence members of the Cep OB3b star-forming region.
