- ID:
- ivo://CDS.VizieR/J/ApJ/887/19
- Title:
- DECam phot. of Gaia stars in Price-Whelan 1
- Short Name:
- J/ApJ/887/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a young ({tau}~117Myr), low-mass (M~1200M_{sun}_), metal-poor ([Fe/H]~-1.14) stellar association at a heliocentric distance D~28.7kpc, placing it far into the Milky Way (MW) halo. At its present Galactocentric position (R,z)~(23,15)kpc, the association is (on the sky) near the leading arm of the gas stream emanating from the Magellanic Cloud system, but is located ~60{deg} from the Large Magellanic Cloud center on the other side of the MW disk. If the cluster is colocated with HI gas in the stream, we directly measure the distance to the leading arm of the Magellanic stream. The measured distance is inconsistent with Magellanic stream model predictions that do not account for ram pressure and gas interaction with the MW disk. The estimated age of the cluster is consistent with the time of last passage of the leading arm gas through the Galactic midplane; we therefore speculate that this star formation event was triggered by its last disk midplane passage. Most details of this idea remain a puzzle: the Magellanic stream has low column density, the MW disk at large radii has low gas density, and the relative velocity of the leading arm and MW gas is large. However it formed, the discovery of a young stellar cluster in the MW halo presents an interesting opportunity for study. This cluster was discovered with Gaia astrometry and photometry alone, but follow-up DECam photometry was crucial for measuring its properties.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/875/L13
- Title:
- DECam r and i magnitudes in the Fornax 6 cluster
- Short Name:
- J/ApJ/875/L13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Since first noticed by Shapley in 1939, a faint object coincident with the Fornax dwarf spheroidal has long been discussed as a possible sixth globular cluster (GC) system. However, debate has continued over whether this overdensity is a statistical artifact or a blended galaxy group. In this Letter we demonstrate, using deep DECam imaging data, that this object is well resolved into stars and is a bona fide star cluster. The stellar overdensity of this cluster is statistically significant at the level of ~6-6.7{sigma} in several different photometric catalogs including Gaia. Therefore, it is highly unlikely to be caused by random fluctuation. We show that Fornax 6 is a star cluster with a peculiarly low surface brightness and irregular shape, which may indicate a strong tidal influence from its host galaxy. The Hess diagram of Fornax 6 is largely consistent with that of Fornax field stars, but it appears to be slightly bluer. However, it is still likely more metal-rich than most of the GCs in the system. Faint clusters like Fornax 6 that orbit and potentially get disrupted in the centers of dwarf galaxies can prove crucial for constraining the dark matter distribution in Milky Way satellites.
- ID:
- ivo://CDS.VizieR/J/MNRAS/484/5049
- Title:
- DECam Survey of Scorpius Centaurus
- Short Name:
- J/MNRAS/484/5049
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using images taken with the Dark Energy Camera (DECam), the first extensive survey of low mass and substellar objects is made in the ~15-20Myr Upper Centaurus Lupus (UCL) and Lower Centaurus Crux (LCC) subgroups of the Scorpius-Centaurus OB Association (Sco-Cen). Due to the size of our data set (>2Tb), we developed an extensive open source set of python libraries to reduce our images, including astrometry, coaddition, and PSF photometry. Our survey consists of 29x3deg^2^ fields in the UCL and LCC subgroups of Sco-Cen and the creation of a catalogue with over 11 million point sources. We create a prioritized list of UCL and LCC candidate members, with 118 best and another 348 good candidates. We show that the luminosity and mass functions of our low mass and substellar candidates are consistent with measurements for the younger Upper Scorpius subgroup and estimates of a universal IMF, with spectral types ranging from M1 down to L1.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A92
- Title:
- Deep all-sky census of the Hyades
- Short Name:
- J/A+A/531/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of the PPMXL catalogue we perform an all-sky census of the Hyades down to masses of about 0.2M_{sun}_ in a region up to 30pc from the cluster centre. We use the proper motions from PPMXL in the convergent point method to determine probable kinematic members. From 2MASS photometry and CMC14 r'-band photometry, we derive empirical colour-absolute magnitude diagrams and, finally, determine photometric membership for all kinematic candidates. This is the first deep (r'<17) all-sky survey of the Hyades allowing a full three-dimensional analysis of the cluster. The survey is complete down to at least M_{K_s_}_=7.3 or 0.25M_{sun}_. We find 724 stellar systems co-moving with the bulk Hyades space velocity, which represent a total mass of 435M_{sun}_. The tidal radius is about 9pc, and 275M_{sun}_ (364 systems) are gravitationally bound. This is the cluster proper. Its mass density profile is perfectly fitted by a Plummer model with a central density of 2.21M_{sun}_/pc^3^ and a core radius of r_co_=3.10pc, while the half-mass radius is r_h_=4.1pc. There are another 100M_{sun}_ in a volume between one and two tidal radii (halo), and another 60M_{sun}_ up to a distance of 30pc from the centre. Strong mass segregation is inherent in the cluster. The present-day luminosity and mass functions are noticeably different in various parts of the cluster (core, corona, halo, and co-movers). They are strongly evolved compared to presently favoured initial mass functions. The analysis of the velocity dispersion of the cluster shows that about 20% of its members must be binaries. As a by-product, we find that presently available theoretical isochrones are not able to adequately describe the near-infrared colour-absolute magnitude relation for those cluster stars that are less massive than about 0.6M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/AJ/155/110
- Title:
- Deep CFHT imaging of VVDS-F22 field. II. Quasars
- Short Name:
- J/AJ/155/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a faint quasar survey in a one-square-degree field. The aim is to test the Y-K/g-z and J-K/i-Y color selection criteria for quasars at faint magnitudes to obtain a complete sample of quasars based on deep optical and near-infrared color-color selection and to measure the faint end of the quasar luminosity function (QLF) over a wide redshift range. We carried out a quasar survey based on the Y-K/g-z and J-K/i-Y quasar selection criteria, using the deep Y-band data obtained from our CFHT/WIRCam Y-band images in a two-degree field within the F22 field of the VIMOS VLT deep survey, optical co-added data from Sloan Digital Sky Survey Stripe 82 and deep near-infrared data from the UKIDSS Deep Extragalactic Survey in the same field. We discovered 25 new quasars at 0.5<z<4.5 and i<22.5 mag within one-square-degree field. The survey significantly increases the number of faint quasars in this field, especially at z~2-3. It confirms that our color selections are highly complete in a wide redshift range (z<4.5), especially over the quasar number density peak at z~2-3, even for faint quasars. Combining all previous known quasars and new discoveries, we construct a sample with 109 quasars and measure the binned QLF and parametric QLF. Although the sample is small, our results agree with a pure luminosity evolution at lower redshift and luminosity evolution and density evolution model at redshift z>2.5.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/20
- Title:
- Deep Chandra survey of the SMC. III. HMXBs
- Short Name:
- J/ApJ/887/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled the most complete census of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low-metallicity environment. In total, we use 123 X-ray sources with detections in our Chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by Haberl & Sturm (2016, J/A+A/586/A81) that fall within the XVP area, but are neither detected in our survey (nine sources) nor matched with any of the 127 sources identified in the XVP data (five sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to (a) the number of OB stars, (b) the local star formation rate (SFR), and (c) the stellar mass produced during the specific star formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to ~40-60Myr, and then gradually decreases. The formation efficiency peaks at ~30-40Myr with average rates of N(HMXB)/SFR=339_-83_^+78^(M_{sun}_/yr)^-1^, and N(HMXB)/M*=(8.74_-0.92_^+1.0^)x10^-6^M_{sun}_^-1^, in good agreement with previous estimates of the average formation efficiency in the broad ~20-60Myr age range.
- ID:
- ivo://CDS.VizieR/J/ApJ/654/915
- Title:
- Deep FORS1 BR photometry of omega Cen
- Short Name:
- J/ApJ/654/915
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep photometric survey performed with the VLT FORS1 aimed at investigating the complex main-sequence structure of the stellar system Centauri. We confirm the presence of a double main sequence and identify its blue component (bMS) over a large field of view up to 26' from the cluster center. We found that bMS stars are significantly more concentrated toward the cluster center than the other "normal" MS stars. The bMS morphology and its position in the CMD have been used to constrain the helium overabundance required to explain the observed MS morphology.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/100
- Title:
- Deep GALEX NUV survey of the Kepler field. I.
- Short Name:
- J/ApJ/813/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report observations of a deep near-ultraviolet (NUV) survey of the Kepler field made in 2012 with the Galaxy Evolution Explorer (GALEX) Complete All-Sky UV Survey Extension (CAUSE). The GALEX-CAUSE Kepler survey (GCK) covers 104 square degrees of the Kepler field and reaches a limiting magnitude of NUV~=22.6 at 3{sigma}. Analysis of the GCK survey has yielded a catalog of 660928 NUV sources, of which 475164 are cross-matched with stars in the Kepler Input Catalog. Approximately 327 of 451 confirmed exoplanet host stars and 2614 of 4696 candidate exoplanet host stars identified by Kepler have NUV photometry in the GCK survey. The GCK catalog should enable the identification and characterization of UV-excess stars in the Kepler field (young solar-type and low-mass stars, chromospherically active binaries, white dwarfs, horizontal branch stars, etc.), and elucidation of various astrophysics problems related to the stars and planetary systems in the Kepler field.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A117
- Title:
- Deep Herschel PACS point spread functions
- Short Name:
- J/A+A/591/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The knowledge of the point spread function (PSF) of imaging instruments represents a fundamental requirement for astronomical observations. The Herschel PACS PSFs delivered by the instrument control centre are obtained from observations of the Vesta asteroid, providing a characterisation of the central part therefore excluding fainter features. However, inumany cases information on both the core and the wings of the PSFs is needed. With this aim, we combine Vesta and Mars dedicated observations and obtain PACS PSFs with an unprecedented dynamic range (~10^6^), at slow and fast scan speeds and for the three photometric bands.
- ID:
- ivo://CDS.VizieR/J/ApJ/743/64
- Title:
- Deep infrared photometry of {sigma} Ori cluster
- Short Name:
- J/ApJ/743/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep I, Z photometric survey covering a total area of 1.12deg^2^ of the {sigma} Orionis cluster and reaching completeness magnitudes of I=22 and Z=21.5mag. From I, I-Z color-magnitude diagrams we have selected 153 candidates that fit the previously known sequence of the cluster. They have magnitudes in the range I=16-23mag, which corresponds to a mass interval from 0.1 down to 0.008M_{sun}_ at the most probable age of {sigma} Orionis (2-4Myr). Using J-band photometry, we find that 124 of the 151 candidates within the completeness of the optical survey (82%) follow the previously known infrared photometric sequence of the cluster and are probably members. We have studied the spatial distribution of the very low mass stars and brown dwarf population of the cluster and found that there are objects located at distances greater than 30 arcmin to the north and west of {sigma} Orionis that probably belong to different populations of the Orion's Belt. For the 102 bona fide {sigma} Orionis cluster member candidates, we find that the radial surface density can be represented by a decreasing exponential function ({sigma}={sigma}_0_e^-r/r_0_^) with a central density of {sigma}_0_=0.23+/-0.03 objects arcmin^-2^ and a characteristic radius of r_0_=9.5+/-0.7 arcmin. Using near-infrared JHK-band data from Two Micron All Sky Survey and UKIRT Deep Infrared Sky Survey and mid-infrared data from Infrared Array Camera/Spitzer, we find that about 5%-9% of the brown dwarf candidates in the {sigma} Orionis cluster have K-band excesses and 30%+/-7% of them show mid-infrared excesses at wavelengths longer than 5.8um. These are probably related to the presence of disks, most of which are "transition disks".