- ID:
- ivo://CDS.VizieR/J/A+A/534/A10
- Title:
- HST/NICMOS III imaging in Orion Nebula Cluster
- Short Name:
- J/A+A/534/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep HST/NICMOS Camera 3 F110W and F160W imaging of a 26'x33', corresponding to 3.1x3.8pc^2^, non-contiguous field towards the Orion Nebula Cluster (ONC). The main aim is to determine the ratio of low-mass stars to brown dwarfs for the cluster as a function of radius out to a radial distance of 1.5pc. The sensitivity of the data outside the nebulous central region is F160W<=21.0mag, significantly deeper than previous studies of the region over a comparable area. We create an extinction limited sample and determine the ratio of low-mass stars (0.08-1M_{sun}_) to brown dwarfs (0.02-0.08M_{sun}_ and 0.03-0.08M_{sun}_) for the cluster as a whole and for several annuli. The ratio found for the cluster within a radius of 1.5pc is R_02_=N(0.08-1M_{sun}_)/N(0.02-0.08M_{sun}_)=1.7+/-0.2, and R_03_=N(0.08-1M_{sun}_)/N(0.03-0.08M_{sun}_)=2.4+/-0.2, after correcting for field stars. The ratio for the central 0.3x0.3pc^2^ region down to 0.03M_{sun}_ was previously found to be R_03_=3.3^+0.8^_-0.7_, suggesting the low-mass content of the cluster is mass segregated. We discuss the implications of a gradient in the ratio of stars to brown dwarfs in the ONC in the context of previous measurements of the cluster and for other nearby star forming regions. We further discuss the current evidence for variations in the low-mass IMF and primordial mass segregation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/541/977
- Title:
- HST observations of low-mass stars in IC 348
- Short Name:
- J/ApJ/541/977
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the low-mass population of the young cluster IC 348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrowband imaging, that measure the strength of the 1.9{mu}m water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from ~0.7 to 0.015M_{sun}_. The mass function derived for the cluster in this interval, dN/dlogM{prop.to}M^0.5^, is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby Sunlike stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation versus as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/448/179
- Title:
- HST photometry in R136
- Short Name:
- J/ApJ/448/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed Hubble Space Telescope (HST) images of the compact, luminous star cluster R136 in the LMC that were taken with the refurbished HST and new Wide Field/Planetary Camera. These images allow us to examine the stellar population in a region of unusually intense star formation at a scale of 0.01pc. We have detected stars to 23.5 in F555W and have quantified the stellar population to an M_555.0 of 0.9 or a mass of 2.8M_{sun}_. Comparisons of HR diagrams with isochrones that were constructed for the HST flight filter system from theoretical stellar evolutionary tracks reveal massive stars, a main sequence to at least 2.8M_{sun}_, and stars with M_555.0>=0.5 still on pre-main sequence tracks. The average stellar population is fit with a 3-4Myr isochrone. Contrary to expectations from star formation models, however, the formation period for the massive stars and lower mass stars appear to largely overlap. We have measured the IMF for stars 2.8-15M_{sun}_ in three annuli from 0.5-4.7pc from the center of the cluster. The slopes of the IMF in all three annuli are the same within the uncertainties, thus, showing no evidence for mass segregation beyond 0.5pc. Furthermore, the combined IMF slope, -1.22+/-0.06, is close to a normal Salpeter IMF. The lower mass limit must be lower than the limits of our measurements: <=2.8M_{sun}_ beyond 0.5pc and <=7M_{sun}_ within 0.1pc. This is contrary to some predictions that the lower mass limit could be as high as 10M_{sun}_ in regions of intense massive star formation. Integrated properties of R136 are consistent with its being comparable to a rather small globular cluster when such clusters were the same age as R136. From the surface brightness profile, an upper limit for core radius of 0.02pc is set. Within a radius of 0.4pc we estimate that there have been roughly 20 crossing times and relaxation should be well along. Within 0.5pc crowding prevents us from detecting the intermediate mass population, but there is a hint of an excess of stars brighter than M_555.0=-5 and of a deficit in the highest mass stars between 0.6pc and 1.2pc. This would be consistent with dynamical segregation.
- ID:
- ivo://CDS.VizieR/J/AJ/147/4
- Title:
- HST photometry of 5 globular clusters
- Short Name:
- J/AJ/147/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quantified and calibrated the metallicity and temperature sensitivities of colors derived from nine Wide-Field Camera 3 filters on board the Hubble Space Telescope using Dartmouth isochrones and Kurucz atmosphere models. The theoretical isochrone colors were tested and calibrated against observations of five well studied galactic clusters, M92, NGC 6752, NGC 104, NGC 5927, and NGC 6791, all of which have spectroscopically determined metallicities spanning -2.30<[Fe/H]<+0.4. We found empirical corrections to the Dartmouth isochrone grid for each of the following color-magnitude diagrams (CMDs): (F555W-F814W, F814W), (F336W-F555W, F814W), (F390M-F555W, F814W), and (F390W-F555W, F814W). Using empirical corrections, we tested the accuracy and spread of the photometric metallicities assigned from CMDs and color-color diagrams (which are necessary to break the age-metallicity degeneracy). Testing three color-color diagrams [(F336W-F555W),(F390M-F555W),(F390W-F555W), versus (F555W-F814W)], we found the colors (F390M-F555W) and (F390W-F555W) to be the best suited to measure photometric metallicities. The color (F390W-F555W) requires much less integration time, but generally produces wider metallicity distributions and, at very low metallicity, the metallicity distribution function (MDF) from (F390W-F555W) is ~60% wider than that from (F390M-F555W). Using the calibrated isochrones, we recovered the overall cluster metallicity to within ~0.1dex in [Fe/H] when using CMDs (i.e., when the distance, reddening, and ages are approximately known). The measured MDF from color-color diagrams shows that this method measures metallicities of stellar clusters of unknown age and metallicity with an accuracy of ~0.2-0.5dex using F336W-F555W, ~0.15-0.25dex using F390M-F555W, and ~0.2-0.4dex with F390W-F555W, with the larger uncertainty pertaining to the lowest metallicity range.
- ID:
- ivo://CDS.VizieR/J/AJ/151/23
- Title:
- HST photometry of stars in HD 97950
- Short Name:
- J/AJ/151/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use photometry in the F220W, F250W, F330W, F435W filters from the High Resolution Channel of the Advanced Camera for Surveys and photometry in the F555W, F675W, and F814W filters from the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope to derive individual stellar reddenings and extinctions for stars in the HD97950 cluster in the giant HII region NGC 3603. The mean line of sight reddening for about a hundred main-sequence member stars inside the cluster is E(F435W-F555W)=1.33+/-0.12mag. After correcting for foreground reddening, the total to selective extinction ratio is R_F555W_=3.75+/-0.87 in the cluster. Within the standard deviation associated with E({lambda}-F555W)/E(F435W-F555W) in each filter, the cluster extinction curve at ultraviolet wavelengths tends to be grayer than the average Galactic extinction laws from Cardelli et al. and Fitzpatrick. It is closer to the extinction law derived by Calzetti et al. for starburst galaxies, where the 0.2175{mu}m bump is absent. This indicates an anomalous extinction in the HD97950 cluster, which may due to the clumpy dust distribution within the cluster, and the size of dust grains being larger than the average Galactic ISM.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/10
- Title:
- HST Treasury Program on the ONC
- Short Name:
- J/ApJS/207/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope (HST) Treasury Program on the Orion Nebula Cluster (ONC) has used 104 orbits of HST time to image the Great Orion Nebula region with the Advanced Camera for Surveys (ACS), the Wide-Field/Planetary Camera 2 (WFPC2), and the Near-Infrared Camera and Multi-Object Spectrograph (NICMOS) instrument in 11 filters ranging from the U band to the H band equivalent of HST. The program has been intended to perform the definitive study of the stellar component of the ONC at visible wavelengths, addressing key questions like the cluster initial mass function, age spread, mass accretion, binarity, and circumstellar disk evolution. The scanning pattern allowed us to cover a contiguous field of approximately 600 arcmin2 with both ACS and WFPC2, with a typical exposure time of approximately 11 minutes per ACS filter, corresponding to a point source depth AB(F435W) = 25.8 and AB(F775W) = 25.2 with 0.2 mag of photometric error. We describe the observations, data reduction, and data products, including images, source catalogs, and tools for quick look preview. In particular, we provide ACS photometry for 3399 stars, most of them detected at multiple epochs; WFPC2 photometry for 1643 stars, 1021 of them detected in the U band; and NICMOS JH photometry for 2116 stars. We summarize the early science results that have been presented in a number of papers.
- ID:
- ivo://CDS.VizieR/J/A+A/391/857
- Title:
- HST UV,V,I photometry of NGC7673 star clusters
- Short Name:
- J/A+A/391/857
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the star cluster system in the starburst galaxy NGC 7673 using archival Hubble Space Telescope WFPC2 broad-band images. For the first time we are able to examine the internal structures of the prominent optical clumps in this galaxy. The clumps are composed of young stars, 16-33% of which are in bright star clusters. We identify 268 star cluster candidates in both the F555W and F814W images, and 50 clusters with the F255W filter. These data allow us to estimate ages and masses using color-magnitude and two-color diagrams for our sample. We find a population of young, <6Myr clusters located throughout the galaxy with concentrations in the clumps. Star cluster mass estimates are 5-50x10^4^M_{sun}_ for the brightest objects. The starburst remains active in physically well-separated regions, indicating a widespread starburst trigger. We discuss clump lifetimes, their implications for the future evolution of NGC 7673, and possible relationships to high redshift starbursts.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/73
- Title:
- HST VI photometry of HD 97950 cluster members stars
- Short Name:
- J/ApJ/764/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep Hubble Space Telescope/Wide Field and Planetary Camera 2 photometry of the young HD 97950 star cluster in the giant H II region NGC 3603. The data were obtained in 1997 and 2007 permitting us to derive membership based on proper motions of the stars. Our data are consistent with an age of 1 Myr for the HD 97950 cluster. A possible age spread, if present in the cluster, appears to be small. The global slope of the incompleteness-corrected mass function for member stars within 60" is {Gamma}=-0.88+/-0.15, which is flatter than the value of a Salpeter slope of -1.35. The radially varying mass function shows pronounced mass segregation ranging from slopes of -0.26 +/-0.32 in the inner 5" to -0.94+/-0.36 in the outermost annulus (40"-60"). Stars more massive than 50M_{sun}_ are found only in the cluster center. The {Lambda} minimum spanning tree technique confirms significant mass segregation down to 30M_{sun}_. The dependence of {Lambda} on mass, i.e., that high-mass stars are more segregated than low-mass stars, and the (weak) dependence of the velocity dispersion on stellar mass might imply that the mass segregation is dynamical in origin. While primordial segregation cannot be excluded, the properties of the mass segregation indicate that dynamical mass segregation may have been the dominant process for segregation of high-mass stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/730/78
- Title:
- Hubble and Spitzer photometry of NGC 602
- Short Name:
- J/ApJ/730/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical (HST/ACS F555W, F814W, and SMARTS/ANDICAM V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8um and MIPS 24um). Combining this with Infrared Survey Facility near-infrared photometry (J, H, Ks), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared. We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ~565 PMS candidates, low-mass Stage III YSOs. We characterize ~40 YSOs by fitting their spectral energy distributions to a grid of models (Robitaille et al. 2007ApJS..169..328R) to derive luminosities, masses, and evolutionary phase (Stages I-III). The higher resolution HST images reveal that ~70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star formation rate of ~0.2-1.0M_{sun}_/yr/kpc^2^, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region.
- ID:
- ivo://CDS.VizieR/J/A+A/481/661
- Title:
- Hyades brown dwarfs and very low mass stars
- Short Name:
- J/A+A/481/661
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a search for brown dwarfs (BDs) and very low mass (VLM) stars in the 625Myr-old Hyades cluster in order to derive the cluster's mass function across the stellar-substellar boundary. We performed a deep (I=23, z=22.5) photometric survey over 16deg^2^ around the cluster center and followed up with K-band photometry to measure the proper motion of candidate members and with optical and near-IR spectroscopy of probable BD and VLM members.
