We present the results of deep near-infrared observations searching for very low mass young stellar objects (YSOs) in the massive star-forming region of S106 taken with the Subaru Telescope. The survey, whose limiting magnitude exceeds 20mag in the JHK' bands, is sensitive enough to provide unprecedented details in the two nebular lobes. In addition, it reveals a census of the stellar population down to objects below the deuterium-burning limit, a fiducial boundary between brown dwarfs and planetary-mass objects. Based on color-color diagrams, nearly 600 embedded YSO candidates with near-infrared excesses have been identified in an area of ~5'x5' that are not uniformly distributed but centrally concentrated.
We present a near-infrared band-merged photometric and polarimetric catalog for the 39'x69' fields in the northeastern part of the Large Magellanic Cloud (LMC), which were observed using SIRPOL, an imaging polarimeter of the InfraRed Survey Facility. This catalog lists 1858 sources brighter than 14mag in the H band with a polarization signal-to-noise ratio greater than three in the J, H, or K_s_ bands. Based on the relationship between the extinction and the polarization degree, we argue that the polarization mostly arises from dichroic extinctions caused by local interstellar dust in the LMC. This catalog allows us to map polarization structures to examine the global geometry of the local magnetic field, and to show a statistical analysis of the polarization of each field to understand its polarization properties. In the selected fields with coherent polarization position angles, we estimate magnetic field strengths in the range of 3-25{mu}G using the Chandrasekhar-Fermi method. This implies the presence of large-scale magnetic fields on a scale of around 100 parsecs. When comparing mid- and far-infrared dust emission maps, we confirmed that the polarization patterns are well aligned with molecular clouds around the star-forming regions.
We present new near-infrared spectroscopic observations of the outer edges of the young stellar cluster around the supermassive black hole at the Galactic center. The observations show a break in the surface density profile of young stars at ~13" (0.52pc). These observations spectroscopically confirm previous suggestions of a break based on photometry. Using Gemini North's Near-Infrared Integral Field Spectrometer, we are able to detect and separate early- and late-type stars with a 75% completeness at K_s_=15.5. We sample a region with radii between 7" and 23" (0.28-0.92pc) from Sgr A* and present new spectral classifications of 144 stars brighter than K_s_=15.5, where 140 stars are late-type (>1Gyr) and only four stars are early-type (young, 4-6Myr). A broken power-law fit of the early-type surface density matches well with our data and previously published values. The projected surface density of late-type stars is also measured and found to be consistent with previous results. We find that the observed early-type surface-density profile is inconsistent with the theory of young stars originating from a tightly bound infalling cluster, as no significant trail of young stars is found at radii above 13". We also note that either a simple disk instability criterion or a cloud-cloud collision could explain the location of the outer edge, though we lack information to make conclusive remarks on either alternative. If this break in surface density represents an edge to the young stellar cluster, it would set an important scale for the most recent episode of star formation at the Galactic center.
NIR spectroscopy of Galactic Wolf-Rayet stars. II.
Short Name:
J/AJ/143/149
Date:
21 Oct 2021
Publisher:
CDS
Description:
We are continuing a J, K and narrowband imaging survey of 300{deg}^2^ of the plane of the Galaxy, searching for new Wolf-Rayet (W-R) stars. Our survey spans 150{deg} in Galactic longitude and reaches 1{deg} above and below the Galactic plane. The survey has a useful limiting magnitude of K=15 over most of the observed Galactic plane, and K=14 (due to severe crowding) within a few degrees of the Galactic center. Thousands of emission-line candidates have been detected. In spectrographic follow-ups of 146 relatively bright W-R star candidates, we have re-examined 11 previously known WC and WN stars and discovered 71 new W-R stars, 17 of type WN and 54 of type WC. Our latest image analysis pipeline now picks out W-R stars with a 57% success rate. Star subtype assignments have been confirmed with the K-band spectra and distances approximated using the method of spectroscopic parallax. Some of the new W-R stars are among the most distant known in our Galaxy. The distribution of these new W-R stars is beginning to trace the locations of massive stars along the distant spiral arms of the Milky Way.
A new method of image subtraction is applied to images from a J, K, and narrow-band imaging survey of 300 deg2 of the plane of the Galaxy, searching for new Wolf-Rayet (WR) stars. Our survey spans 150{deg} in Galactic longitude and reaches b=+/-1{deg} with respect to the Galactic plane. The survey has a useful limiting magnitude of K=15 over most of the observed Galactic plane, and K=14 (due to severe crowding) within a few degrees of the Galactic Centre. The new image subtraction method described here (better than aperture or even point-spread-function photometry in very crowded fields) detected several thousand emission-line candidates. In 2011 and 2012 June and July, we spectroscopically followed up on 333 candidates with MDM-TIFKAM and Infrared Telescope Facility (IRTF)-SpeX, discovering 89 emission-line sources. These include 49 WR stars, 43 of them previously unidentified, including the most distant known Galactic WR stars, more than doubling the number on the far side of the Milky Way. We also demonstrate our survey's ability to detect very faint planetary nebulae and other NIR emission objects.
We present JHKs observations of the metal-poor ([Fe/H]{<}-1.40) dwarf-irregular galaxies, Leo A and Sextans A, obtained with the WIYN High-resolution Infrared Camera at Kitt Peak. Their near-IR stellar populations are characterized by using a combination of color-magnitude diagrams and by identifying long-period variable stars. We detected red giant and asymptotic giant branch stars, consistent with membership of the galaxy's intermediate-age populations (2-8Gyr old). Matching our data to broadband optical and mid-IR photometry, we determine luminosities, temperatures, and dust-production rates (DPR) for each star. We identify 32 stars in LeoA and 101 stars in Sextans A with a DPR>10^-11^M_{sun}_/yr, confirming that metal-poor stars can form substantial amounts of dust. We also find tentative evidence for oxygen-rich dust formation at low metallicity, contradicting previous models that suggest oxygen-rich dust production is inhibited in metal-poor environments. The total rates of dust injection into the interstellar medium of Leo A and Sextans A are (8.2+/-1.8)x10^-9^M_{sun}_/yr and (6.2+/-0.2)x10^-7^M_{sun}/yr, respectively. The majority of this dust is produced by a few very dusty evolved stars and does not vary strongly with metallicity.
We present a near-infrared survey for the visual multiples in the Orion molecular clouds region at separations between 100 and 1000au. These data were acquired at 1.6um with the NICMOS and WFC3 cameras on the Hubble Space Telescope. Additional photometry was obtained for some of the sources at 2.05um with NICMOS and in the L' band with NSFCAM2 on NASA's InfraRed Telescope Facility. Toward 129 protostars and 197 pre-main-sequence stars with disks observed with WFC3, we detect 21 and 28 candidate companions between the projected separations of 100-1000au, of which less than 5 and 8, respectively, are chance line-of-sight coincidences. The resulting companion fraction (CF) after the correction for the line-of-sight contamination is 14.4_-1.3_^+1.1^ for protostars and 12.5_-0.8_^+1.2^ for the pre-main-sequence stars. These values are similar to those found for main-sequence stars, suggesting that there is little variation in the CF with evolution, although several observational biases may mask a decrease in the CF from protostars to the main-sequence stars. After segregating the sample into two populations based on the surrounding surface density of young stellar objects, we find that the CF in the high stellar density regions ({Sigma}_YSO_>45pc^-2^) is approximately 50% higher than that found in the low stellar density regions ({Sigma}_YSO_<45pc^-2^). We interpret this as evidence for the elevated formation of companions at 100-1000 au in the denser environments of Orion. We discuss possible reasons for this elevated formation.
The infrared photometric study of SDSS selected Narrow Line Seyfert 1 Galaxies (NLS1s) is presented in this paper. We have made cross-identifications for such NLS1s with 2MASS and WISE observations. Finally 992 NLS1s have 2MASS and WISE counterparts. Comparisons of NLS1s with the Broad Line Seyfert 1 (BLS1s) and Seyfert 2 galaxies are made. It is shown that from 1um to 5um NLS1s are redder than BLS1s and Seyfert 2 galaxies possibly due to the richer dust environment in NLS1 nuclei or to the orientation effect while in the longer wavelengths those three kinds of sources have quite similar behavior indicative of radiation mainly from the similar warm starburst-related dust and the related AGN dust. In addition, relations between infrared colors and related (to H{beta}) strengths of some important lines are also investigated. The results show that the related strengths of [FeII] 4570{AA} are positively correlated with infrared colors in the 1-5um region, but negatively correlated with infrared colors in the 12-22um region; the related strength of [OIII] 5007{AA} are negatively correlated with infrared colors in the 1-5um region, but positively correlated with infrared colors in the 12-22um region; the related strength of [NII]6583{AA} are also negatively correlated with infrared colors in the 1-5um region, but positively correlated with infrared colors in the 12-22um region. Therefore it is indicated that the behavior of [FeII] 4570{AA} is just opposed to that for [OIII] 5007{AA} and [NII] 6583{AA} This result may be caused by different origins of such lines.
Measurements of the {lambda}4200{AA} CN band are presented for 712 late-type stars. G band data are also included for 212 of these stars. Mean errors of absolute magnitudes derived from CN intensities are at least 1.5 mag. Spectral type determined by G band intensity has a mean deviation of 0.15 class from the MK type for G to K1 stars. The file photom.dat contains 712 data records in the form of CN ratios and G-band ratios, with annotations. The CN ratio is the ratio of the sum of the intensities in the 4097-4149{AA} and 4230-4283{AA} wavelength ranges to the intensity in the 4164-4214{AA} range. The latter contains the CN absorption band, and the first two ranges serve as nearby continuum references. The ratio is a measure of the depth of the absorption in the CN band. Values greater than 2 indicate absorption in the band. The G-band ratio is similarly the ratio of the sum of the intensities in the 4230-4270{AA} and 4342-4380{AA} wavelength ranges to the intensity in the 4285-4315{AA} range.
This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8Gyr and masses close to the canonical 0.6M_{sun}_.
