A WIDE-FIELD SURVEY OF THE ORION NEBULA CLUSTER IN THE NEAR-INFRARED

Aims. We have analyzed optical spectra of 25 X-ray sources identified as potential new members of the Taurus molecular cloud (TMC), in order to confirm their membership in this star-forming region. Methods. Fifty-seven candidate members were previously selected among the X-ray sources in the XEST survey, having a 2MASS counterpart compatible with a pre-main sequence star based on color-magnitude and color-color diagrams. We obtained high-resolution optical spectra for 7 of these candidates with the SARG spectrograph at the TNG telescope, which were used to search for lithium absorption and to measure the Ha line and the radial and rotational velocities. Then, 18 low-resolution optical spectra obtained with the instrument DOLORES for other candidate members were used for spectral classification, for Hα measurements, and to assess membership together with IR color-color and color-magnitude diagrams and additional information from the X-ray data. Results. We found that 3 sources show lithium absorption, with equivalent widths (EWs) of ∼500 mA, broad spectral line profiles, indicating rotational velocities of ∼20-40 km s -1 , radial velocities consistent with those for known members, and Ha emission. Two of them are classified as new weak-lined T Tauri stars, while the EW (∼-9 A) of the Ha line and its broad asymmetric profile clearly indicate that the third star (XEST-26-062) is a classical T Tauri star. Fourteen sources observed with DOLORES are M-type stars. Fifteen sources show Ha emission. Six of them have spectra that indicate surface gravity lower than in main sequence stars, and their de-reddened positions in IR color-magnitude diagrams are consistent with their derived spectral type and with pre-main sequence models at the distance of the TMC. The K-type star XEST-11-078 is confirmed as a new member on the basis of the strength of the Hα emission line. Overall, we confirm membership to the TMC for 10 out of 25 X-ray sources observed in the optical. Three sources remain uncertain.

view Abstract Citations (83) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Deep CCD photometry in globular clusters. I. The main sequence of M 4. Richer, H. B. ; Fahlman, G. G. Abstract Color-magnitude and color-color diagrams have been constructed for a 4 x 3-arcmin field of the globular cluster M4, on the basis of deep UBV CCD images. The color-magnitude diagram indicates that the main sequence, down to almost 3 mag below the turnoff, has an intrinsic width no greater than + or 0.02 mag in (B-V), implying either that the variation in He abundance in these stars must be less than + or - 0.07, or that the fractional variation in metallicity is not larger than + or - 0.22. Field stars in the direction of the cluster yield E(B-V) of 0.37 + or - 0.06, while the best present metallicity estimate for M4 is -0.93 + or - 0.31. The corresponding isochrones from VandenBerg (1983) are found to be in excellent general agreement with the present data. Publication: The Astrophysical Journal Pub Date: February 1984 DOI: 10.1086/161688 Bibcode: 1984ApJ...277..227R Keywords: Abundance; Globular Clusters; Main Sequence Stars; Stellar Evolution; Stellar Spectrophotometry; Ubv Spectra; Charge Coupled Devices; Color-Color Diagram; Color-Magnitude Diagram; Distance; Interstellar Extinction; Metallicity; Stellar Color; Stellar Magnitude; Astronomy full text sources ADS | data products SIMBAD (9) Related Materials (7) Part 2: 1985ApJS...58..225F Part 3: 1986ApJ...304..273R Part 4: 1987ApJ...316..189R Part 5: 1988ApJ...325..218R Part 6: 1988ApJ...329..187R Part 7: 1989AJ.....98.1335S Part 8: 1989AJ.....98.2124H

RCW 34 is a special star-forming region with a few stars showing an infrared excess, but seems as if it has an uncommon abundance in T Tauri stars. This possibility was confirmed by (i) clustering of classical T Tauri (CTT) stars in the two-color diagram, (ii) clustering of pre-main-sequence stars in the color–magnitude diagram, as well as (iii) the significant clustering at dimensions larger than the image-frame size, indicated by the second ‘bump’ in the two-point correlation analysis. A possible explanation for the above features could be the existence of an underlying wide CTT cluster with a smaller cluster centered around the massive star. The Ks-band luminosity function (α = 0.31) of RCW 34 shows that it is indeed a region of low stellar masses with an age of about of 1 Myr. Spectroscopic confirmation of such an underlying T Tauri cluster is necessary before any definite conclusions can be reached.

view Abstract Citations (24) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Late-Type Stars in an Inner and Far Disk Field of M31 Richer, Harvey B. ; Crabtree, Dennis R. ; Pritchet, Christopher J. Abstract Two disk fields in M31, one in Baade's field IV at 20 kpc from the nucleus of the galaxy and the other at 4 kpc, were surveyed for late-type stars using broad-band V and I filters (both fields) as well as narrow-band filters in the outer field. The carbon to late M star ratio in the outer field was found to be 0.15, almost identical to that in a field at 11 kpc studied earlier. The color-magnitude diagrams for both fields were constructed. The diagram for the outer field clearly shows a giant branch which extends well to the red of that of the most metal-rich globular cluster. The carbon stars occupy a relatively unique position in this diagram, being in general the most luminous objects in the field. The widths of the giant branches in both fields are much wider than can be accounted for by photometric errors. The most likely reason for this in the outer field is that stars with a range in mass of about a factor of 2 are funneling into this region of the color-magnitude diagram. Asymptotic giant branch (AGB) luminosity functions were assembled for the inner and outer fields and compared with that for a field at 11 kpc studied in an earlier paper. The functions in the outer two fields are identical within the errors, but the inner field exhibits a lack of luminous AGB stars together with an excess of faint ones. Finally, the distance to M31 is determined using the carbon stars. A true distance modulus of 24.45 is found. Publication: The Astrophysical Journal Pub Date: June 1990 DOI: 10.1086/168779 Bibcode: 1990ApJ...355..448R Keywords: Andromeda Galaxy; Carbon Stars; M Stars; Asymptotic Giant Branch Stars; Color-Color Diagram; Color-Magnitude Diagram; Distance; Galactic Structure; Stellar Luminosity; Astrophysics; GALAXIES: DISTANCES; GALAXIES: INDIVIDUAL MESSIER NUMBER: M31; GALAXIES: STELLAR CONTENT; STARS: CARBON full text sources ADS | data products SIMBAD (4) NED (1)

We present time-series photometry of stars located in the extremely young open cluster Berkeley 59. Using the 1.04 m telescope at ARIES, Nainital, we have identified 42 variables in a field of 13'x13' around the cluster. The probable members of the cluster are identified using (V, V-I) colour-magnitude diagram and (J-H, H-K) colour-colour diagram. Thirty one variables are found to be pre-main sequence stars associated with the cluster. The ages and masses of pre-main sequence stars are derived from colour-magnitude diagram by fitting theoretical models to the observed data points. The ages of the majority of the probable pre-main sequence variable candidates range from 1 to 5 Myrs. The masses of these pre-main sequence variable stars are found to be in the range of ~0.3 to ~3.5 Msun and these could be T Tauri stars. The present statistics reveal that about 90% T Tauri stars have periods < 15 days. The classical T Tauri stars are found to have larger amplitude in comparison to the weak line T Tauri stars. There is an indication that the amplitude decreases with increase of the mass, which could be due to the dispersal of disk of relatively massive stars.

We present CCD photometry in the Johnson UBV and Kron-Cousins I systems down to V~ 22.0 for the open clusters NGC 2311, Trumpler 6, NGC 2432 and BH 54 and their surrounding fields. Trumpler 6 and BH 54 have never been studied before and so we provide, for the first time, estimates of their fundamental parameters. We obtained colour-magnitude diagrams (CMDs) and colour-colour diagrams cleaned from field star contamination by statistically subtracting stars in terms of spatial density, magnitude and colour distributions. Cluster angular radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. Using the cleaned CMDs and colour-colour diagrams, we applied sound photometric membership criteria to discriminate cluster members from interloper field stars. The interstellar extinction across the cluster fields derived from the 100-μm dust emission full-sky maps can be considered uniform within the quoted uncertainties. The E(B-V) and E(V-I) colour excesses and the apparent distance moduli of the clusters were estimated from the fit of the zero-age main-sequence to the colour-colour diagrams and CMDs, respectively. Cluster ages were determined from the comparison of the four clusters' CMDs with solar metallicity theoretical isochrones of the Geneva group. All the clusters were found to be moderately young objects, their ages ranging between 60 and 250 Myr. © 2010 The Authors. Journal compilation © 2010 RAS.

A CCD UBVRI survey of northern open clusters is being undertaken at San Pedro Mártir, México, and performed using always the same instrumental setup (telescope, CCD, filters), reduction methods, and system of standards of Landolt (1992). To date more than 300 clusters (mostly unstudied previously) have been observed, and about half the data reduced using aperture-photometry and PSF techniques. Our analysis procedures are being refined by studying in detail a small subset of these clusters. For example, the heavily reddened clusters Be80 and Be95 are being examined in the color-color diagrams: (B-V, U-B) and (B-V, R-I) to better understand the problems of curvature and variable reddening. For clusters for which our U data reaches the F-type stars, such as NGC2192 and NGC7296, techniques are being examined for estimating both the reddening E(B-V) and metallicity [Fe/H] via the use of the (U-B) excess. If the clusters also have “red clump” stars, such as NGC1798 and Do02, these procedures can be iterated between the clump and main sequence stars to establish even better the values of E(B-V) and [Fe/H]. Finally, color-magnitude diagrams, such as (B-V, V) and (V-I, V), are being employed together with the SchmidtKaler (1982) colors and Padova isochrones of Girardi et al. (2000) to obtain distances and ages for these clusters. A java-based computer program is being developed to help in the visualization and analysis of these photometric data. This system is capable of displaying each cluster simultaneously in different color-color and color-magnitude diagrams and has an interactive way to identify a star, or group of stars, in one diagram and to see were it falls in the other diagrams, facilitating the elimination of field stars and the apperception of cluster features. This program is capable of displaying up to 16 different diagrams for one cluster and processing up to 20 clusters at the same time. Our aims are the following: (1) a common UBVRI photometric scale for open clusters, (2) an atlas of color-color and color-magnitude diagrams for open clusters, (3) a homogeneous set of cluster reddenings, distances, and ages, (4) an increased number of old and distant open clusters, and (5) a selection of interesting clusters for further study.

We present multicolour CCD photometry for two poorly studied open clusters (King 5 and Be 20). Photometry for a field near King 5 was also carried out to estimate the contamination by field stars. The colour magnitude diagrams (CMD) of the clusters show a well defined main sequence extending to the limit of the photometry, mag. The reddening for King 5, estimated from the colour-colour diagram, is ~0.82, whereas that for Be 20 as estimated by comparing theoretical main-sequence (MS) with the observed MS is 0.10. The morphology of the CMDs indicates that these clusters are old. The CMD of Be 20 shows a globular cluster-like horizontal branch. In case of King 5 the comparison of observational CMDs with the standard isochrones of VandenBerg ([CITE]) indicates an apparent discrepancy between the shape of the turnoff and isochrones. The CMDs of King 5 seem to be better understood in terms of stellar models with convective overshoot. The comparison of the CMDs with the stellar models by Bertelli et al. ([CITE]) with convective overshoot produces a good fit for a metallicity and an age = 1 Gyr for King 5 and 5 Gyr for Be 20. An apparent distance modulus and 15.1 has been estimated for King 5 and Be 20 respectively. They correspond to a distance of pc and 9026 ± 480 pc, respectively. The radial density distribution in King 5 indicates that there is an excess of low mass stars in the outer region of the cluster, whereas the density distribution in Be 20 shows a good fit with the empirical King ([CITE]) model. For both clusters, observations have also been carried out to search for variable stars.

view Abstract Citations (16) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An investigation of T Tauri variability. Schmelz, J. T. Abstract Three mechanisms have been suggested to account for the photometric variability in T Tauri stars: (1) changes in the effective photospheric spectral type; (2) changes in the optical thickness of the chromosphere; and (3) changes in the optical thickness of the dust shell. The author investigates these processes with color-color diagrams and energy distribution plots of 14 stars located in the Taurus-Auriga dark cloud complex. A relationship between a strong chromosphere and chromospheric variability was found as well as a similar relationship between a thick dust shell and dust shell variability. There is some evidence that the stellar photosphere becomes more stable with increasing age during the T Tauri phase. Publication: The Astronomical Journal Pub Date: January 1984 DOI: 10.1086/113487 Bibcode: 1984AJ.....89..108S Keywords: Chromosphere; Stellar Activity; Stellar Envelopes; Stellar Spectrophotometry; T Tauri Stars; Color-Color Diagram; Optical Thickness; Photosphere; Spectral Energy Distribution; Stellar Color; Stellar Evolution; Stellar Spectra; Variability; Astrophysics; Circumstellar Shells:T Tauri Stars; Stellar Chromospheres:T Tauri Stars; T Tauri Stars:Circumstellar Shells; T Tauri Stars:Stellar Chromospheres; T Tauri Stars:Variations full text sources ADS | data products SIMBAD (15)

Aims. Currently, the global characteristics and evolution of super star clusters (SSCs) are not well understood, due to the large distances to their host galaxies. We aim to study the population of SSCs in IRAS 17138-1017, a luminous infrared galaxy (LIRG), in terms of age, extinction, mass, and luminosity distribution. Methods. We analyzed imaging data in the near-infrared from the GeMS/GSAOI instrument on the Gemini telescope and generated simulations with the radiative transfer code MontAGN. The extraction of SSCs from the images and their photometry in J, H, and Ks allowed us to derive color-color and color-magnitude diagrams. Comparison with a theoretical stellar evolutionary track gives a first hint into the extinction towards each SSC, as well as their ages, despite some degeneracy between those two quantities. Spectra given by our radiative transfer code MontAGN, which includes dust emission, also provide insightful predictions and comparisons. Results. We detect with a fair degree of confidence 54 SSCs of mKs between 16 mag and 21 mag with a median instrumental uncertainty of 0.05 mag. When plotted on a color–color diagram and a color–magnitude diagram, it appears that most of the sources are very much extinct with respect to an intrinsic theoretical evolutionary track. Once de-reddened, the colors point unambiguously to two distinct and very recent starburst episodes at 2.8 and 4.5 Myr. While the SSCs in the 4.5 Myr starburst are distributed along the spiral arms, the 2.8 Myr SSCs are concentrated in the central region. The luminosity and mass functions present a classical power-law behavior, although with shallower slopes than generally observed in LIRGs. Comparison with radiative transfer simulations shows that, the dust thermal emission and scattered light are negligible and could not explain the few very red SSCs that could not be de-reddened safely.

We have begun a survey of the chemical and dynamical properties of the Milky Way disk as traced by open star clusters. In this first contribution, the general goals of our survey are outlined and the strengths and limitations of using star clusters as a Galactic disk tracer sample are discussed. We also present medium resolution (R ~ 15,0000) spectroscopy of open cluster stars obtained with the Hydra multi-object spectrographs on the Cerro Tololo Inter-American Observatory 4-m and WIYN 3.5-m telescopes. Here we use these data to determine the radial velocities of 3436 stars in the fields of open clusters within about 3 kpc, with specific attention to stars having proper motions in the Tycho-2 catalog. Additional radial velocity members (without Tycho-2 proper motions) that can be used for future studies of these clusters were also identified. The radial velocities, proper motions, and the angular distance of the stars from cluster center are used to derive cluster membership probabilities for stars in each cluster field using a non-parametric approach, and the cluster members so-identified are used, in turn, to derive the reliable bulk three-dimensional motion for 66 of 71 targeted open clusters. The high probability cluster members that we identify help to clarify the color-magnitude sequences for many of the clusters, and are prime targets for future echelle resolution spectroscopy as well as astrometric study with the Space Interferometry Mission (SIM Planetquest).

view Abstract Citations (12) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Halpha -emission stars in the young cluster NGC 2264. Rydgren, A. E. Abstract UBVRI photometry is given for a sample of 25 late-type H-alpha-emission stars in the young cluster NGC 2264. The stars are in the V magnitude range from 12 to 16. Some but not all appear to be T Tauri stars. The color-color diagrams support the view that the deviations from normal photospheric colors (due to 'spectral veiling' and line emission) decrease with increasing wavelength between the U and I filters. In the (V, V - R) diagram, the H-alpha-emission stars lie in a well-defined pre-main-sequence band. Within this sample, there is a trend toward stronger line emission and spectral veiling with later spectral type. All of the likely legitimate T Tauri stars have inferred spectral types later than about K3. The question of cluster membership for stars in the cluster field with very small proper motions is considered. Publication: The Astronomical Journal Pub Date: January 1979 DOI: 10.1086/112393 Bibcode: 1979AJ.....84...90R Keywords: Emission Spectra; H Alpha Line; Late Stars; Stellar Spectrophotometry; Ubv Spectra; Color-Color Diagram; Line Spectra; Main Sequence Stars; Photoelectric Emission; Star Clusters; Astrophysics; Late-Type Stars:Open Clusters; Open Clusters:T Tauri Stars full text sources ADS | data products SIMBAD (1)

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year.

view Abstract Citations (308) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy of Galaxies in Distant Clusters. IV. A Catalog of Photometry and Spectroscopy for Galaxies in Seven Clusters with 0.35 < Z < 0.55 Dressler, Alan ; Gunn, James E. Abstract We present photometry and spectroscopy for seven deep fields containing distant clusters of galaxies with 0.35 <z <0.55. Positions and photometric parameters, including r-magnitudes, g - r and r - i colors, surface brightnesses, and photometric profile types are given for ~ 2000 galaxies. We have obtained low-resolution spectroscopy from which redshifts have been determined for 289 objects, of which 190 are cluster members. We classify these according to dominant spectral features and plot examples in each cluster. Color-magnitude and color-color diagrams are formed which show trends in the cluster populations, and maps are made of the cluster field using the color-color relations to increase the contrast of cluster over field. Galaxies with spectra typical of old stellar populations cluster most strongly, with active galaxies, those with recent or ongoing star formation, or an active nucleus, distributed more diffusely. The g - r color is well correlated with active star formation as judged from spectral features. Some other weaker correlations with surface brightness and profile types are briefly discussed. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1992 DOI: 10.1086/191620 Bibcode: 1992ApJS...78....1D Keywords: Astronomical Catalogs; Astronomical Photometry; Astronomical Spectroscopy; Color-Color Diagram; Galactic Clusters; Red Shift; Active Galaxies; Astrometry; Color-Magnitude Diagram; Galactic Evolution; Star Formation; Astronomy; GALAXIES: CLUSTERING; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: PHOTOMETRY full text sources ADS | data products SIMBAD (1977) NED (1942) CDS (2) Related Materials (4) Catalog: 1993yCat..20780001D Part 1: 1982ApJ...263..533D Part 2: 1983ApJ...270....7D Part 3: 1985ApJ...294...70D

We present the first catalogue of point-source UV-excess sources selected from the UVEX survey. UVEX images the Northern Galactic Plane in the U, g, r and HeI5875 bands in the Galactic latitude range -5deg<b<+5deg. Through an automated algorithm, which works on a field-to-field basis, we select blue UV-excess sources in 211 square degrees from the (U-g) vs. (g-r) colour-colour diagram and the g vs. (U-g) and g vs. (g-r) colour-magnitude diagrams. The UV-excess catalogue covers the magnituderange 14<g<22.5, contains 2170 sources and consists of a mix of white dwarfs, post-common-envelope objects, interacting binaries, quasars and AGN. Two other samples of outliers were found during the selection: i) a 'subdwarf' sample, consisting of no less than 9872 candidate metal-poor stars or lightly reddened main-sequence stars, and ii) a 'purple' sample consisting of 803 objects, most likely a mix of reddened late M-giants, T Tauri stars, planetary nebulae, symbiotic stars and carbon stars. Cross-matching the selected UV-excess catalogue with other catalogues aids with the first classification of the different populations and shows that more than 99% of our selected sources are unidentified sources.