- ID:
- ivo://CDS.VizieR/J/MNRAS/433/543
- Title:
- Choirs, HI galaxy groups
- Short Name:
- J/MNRAS/433/543
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- H{alpha} observations centred on galaxies selected from the Hi Parkes All-Sky Survey (HiPASS) typically show one and sometimes two star-forming galaxies within the ~15arcmin beam of the Parkes 64m HI detections. In our Survey for Ionization in Neutral Gas Galaxies (SINGG) we found 15 cases of HiPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case, we found a field with at least nine ELGs. In this paper, we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in HiPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total HI mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, H{alpha} equivalent width and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly Hi deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (SFE; the ratio of star formation rate to HI mass), showing an increasing trend in SFE with stellar mass.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/641/A110
- Title:
- Chromospheric activity of nearby Sun-like stars
- Short Name:
- J/A+A/641/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chromospheric emission in the cores of the CaII H & K lines of late-type dwarfs is a well known indicator of magnetic activity that decreases with increasing stellar age. I use this indicator to investigate the formation history of nearby G- and early K-type stars with origins at galactocentric distances similar to that of the region where the Sun was born. A parent sample of single main-sequence stars with near-solar metallicity and known magnetic activity levels is built from catalogues of stellar atmospheric parameters and chromospheric activity indices. A kinematical approach uses Gaia astrometric data to differentiate thin disc stars from thick disc stars. Measured distributions of R'_HK_ chromospheric activity indices are compared with Monte Carlo simulations based on an empirical model of chromospheric activity evolution. The thin disc includes a significant fraction of Sun-like stars with intermediate activity levels while most early K- and G-type stars from the thick disc are inactive. The chromospheric activity distribution among nearby Sun-like dwarfs from the thin disc can be explained by a combination of an old (>6-7Gyr) star formation event (or events) and a more recent (<3Gyr) burst of star formation. Such an event is not required to account for the R'_HK_ index distributions of nearby thick disc stars. The distribution of magnetic activity among local G- and early K-type stars with a near-solar metallicity bears the imprint of an important star formation event that occurred ~1.9 to 2.6Gyr ago in the thin disc of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A163
- Title:
- CIG 96 deep optical and HI images
- Short Name:
- J/A+A/619/A163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Asymmetries in atomic hydrogen (HI) in galaxies are often caused by the interaction with close companions, making isolated galaxies an ideal framework to study secular evolution. The AMIGA project has demonstrated that isolated galaxies show the lowest level of asymmetry in their HI integrated profiles compared to even field galaxies, yet some present significant asymmetries. CIG 96 (NGC 864) is a representative case reaching a 16% level. Our aim is to investigate the HI asymmetries of the spiral galaxy CIG 96 and what processes have triggered the star-forming regions observed in the XUV pseudo-ring. We performed deep optical observations at CAHA1.23m, CAHA2.2m and VST (OmegaCAM wide-field camera) telescopes. We reach surface brightness (SB) limits of {mu}_CAHA2.2m_=27.5mag/arcsec^2^ (Cousins R) and {mu}_VST_=28.7mag/arcsec^2^ (SDSS r) that show the XUV pseudo-ring of the galaxy in detail. Additionally, a wavelet filtering of the HI data cube from our deep observations with VLA/EVLA telescope allowed us to reach a column density of N_HI_=8.9x10^18^cm^-2^ (5{sigma}) (28"x28" beam), lower than in any isolated galaxy. We confirm that the HI of CIG 96 extends farther than 4xr_25_ in all directions. Furthermore, we detect for the first time two gaseous structures (~10^6^M_{sun}_) in the outskirts. The SDSS g-r colour index image from CAHA1.23m shows extremely blue colours in certain regions of the pseudo-ring where N_HI_>8.5x10^20^cm^-2^, whereas the rest show red colours. Galactic cirrus contaminate the field, setting an unavoidable detection limit at 28.5mag/arcsec^2^ (SDSS r). At the current SB and NHI levels, we detect no stellar link within 1{deg}x1{deg} or gaseous link within 40'x40' between CIG 96 and any companion. The isolation criteria rule out interactions with other similar-sized galaxies for at least 2.7Gyr. Using existing stellar evolution models, the age of the pseudo-ring is estimated at 1Gyr or older. Undetected previously accreted companions and cold gas accretion remain as the main hypothesis to explain the optical pseudo-ring and HI features of CIG 96.
- ID:
- ivo://CDS.VizieR/J/ApJ/898/85
- Title:
- CII emission-line stars in LMC with MagE spectra
- Short Name:
- J/ApJ/898/85
- Date:
- 21 Mar 2022 08:48:14
- Publisher:
- CDS
- Description:
- We present a narrowband imaging survey of the Large Magellanic Cloud (LMC), designed to isolate the CII{lambda}{lambda}7231,7236 emission lines in objects as faint as m_{lambda}7400_~18. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by CII emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged ~50deg^2^ using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known CII emitters were easily recovered, validating the survey design. We find 38 new CII emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding CII emission in each. One is a new [WC11]. Another shows both the narrow CII emission lines characteristic of a [WC11], but also broad emission of CIV, OV, and HeII characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak CII emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous OII transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected CII emitters are largely of an old population.
- ID:
- ivo://CDS.VizieR/J/AJ/119/3026
- Title:
- Circumstellar disk candidates in Orion
- Short Name:
- J/AJ/119/3026
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an optical study of four 45'x45' fields centered ~0.5{deg} east, west, north, and south of the Orion Nebula Cluster center. We have measured V and I_C_ photometry for ~5000 stars, and U photometry for ~1600 of these. We have obtained spectral classifications for ~300 of the stars with UVI_C_ photometry plus an additional ~200 stars located outside the area of our photometric survey. Dereddened photometry allows us to investigate the evidence for circumstellar accretion disks from excess emission at ultraviolet wavelengths, as well as the mass and age distributions of our sample. We find ~230 active accretion disk candidates and estimate the accretion disk fraction at >~40%. We use the magnitude of the ultraviolet excess to infer disk accretion rates. The mass accretion rate (dM/dt) decreases slowly with age over the limited age range spanned by our data, 1-3Myr, and increases slowly with mass over the limited mass range 0.2-1.2 M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/AJ/135/966
- Title:
- Circumstellar disk evolution in NGC 2068/71
- Short Name:
- J/AJ/135/966
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the disk and accretion properties of young stars in the NGC 2068 and NGC 2071 clusters. Using low-resolution optical spectra, we define a membership sample and determine an age for the region of ~2Myr. Using high-resolution spectra of the H{alpha} line we study the accretion activity of these likely members and also examine the disk properties of the likely members using IRAC and MIPS mid-infrared photometry. A substantial fraction (79%) of the 67 members have an infrared excess while all of the stars with significant infrared excess show evidence for active accretion. We find three populations of evolved disks (IRAC weak, MIPS weak, and transition disks) all of which show decreased accretion activity in addition to the evidence for evolution in the dust disk.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A86
- Title:
- Circumstellar disks in Lupus complex
- Short Name:
- J/A+A/642/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous star formation studies have, out of necessity, often defined a population of young stars confined to the proximity of a molecular cloud. Gaia allows us to examine a wider, three-dimensional structure of nearby star forming regions, leading to a new understanding of their history. We present a wide-area survey covering 494 deg^2^ of the Lupus complex, a prototypical low-mass star forming region. Our survey includes all known molecular clouds in this region as well as parts of the Upper Scorpius and Upper Centaurus Lupus (UCL) groups of the Sco-Cen complex. We combine Gaia DR2 proper motions and parallaxes as well as ALLWISE mid-infrared photometry to select young stellar objects (YSOs) with disks. The YSO ages are inferred from Gaia color-magnitude diagrams, and their evolutionary stages from the slope of the spectral energy distributions. We find 98 new disk-bearing sources. Our new sample includes objects with ages ranging from 1 to 15Myr and masses ranging from 0.05 to 0.5M_{sun}_, and consists of 56 sources with thick disks and 42 sources with anemic disks. While the youngest members are concentrated in the clouds and at distances of 160 pc, there is a distributed population of slightly older stars that overlap in proper motion, spatial distribution, distance, and age with the Lupus and UCL groups. The spatial and kinematic properties of the new disk-bearing YSOs indicate that Lupus and UCL are not distinct groups. Our new sample comprises some of the nearest disks to Earth at these ages, and thus provides an important target for follow-up studies of disks and accretion in very low mass stars, for example with ALMA and ESO-VLT X-shooter.
- ID:
- ivo://CDS.VizieR/J/A+A/580/A131
- Title:
- Circumstellar-interacting supernovae
- Short Name:
- J/A+A/580/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some circumstellar-interacting (CSI) supernovae (SNe) are produced by the explosions of massive stars that have lost mass shortly before the SN explosion. There is evidence that the precursors of some SNe IIn were luminous blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been observed before the SN explosion. Eruptive events of massive stars are named SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still unclear. The large variety of observational properties of CSI SNe suggests the existence of other progenitors, such as red supergiant (RSG) stars with superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN progenitors is still largely unexplored. Our goal is to gain insight into the nature of the progenitor stars of CSI SNe by studying their environments, in particular the metallicity at their locations. We obtain metallicity measurements at the location of 60 transients (including SNe IIn, SNe Ibn, and SN IMs) via emission-line diagnostic on optical spectra obtained at the Nordic Optical Telescope and through public archives. Metallicity values from the literature complement our sample. We compare the metallicity distributions among the different CSI SN subtypes, and to those of other core-collapse SN types. We also search for possible correlations between metallicity and CSI SN observational properties. We find that SN IMs tend to occur in environments with lower metallicity than those of SNe IIn. Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower metallicities, similar to those of SN IMs. The metallicity distribution of SNe IIn can be reproduced by combining the metallicity distributions of SN IMs (which may be produced by major outbursts of massive stars like LBVs) and SNe IIP (produced by RSGs). The same applies to the distributions of the normalized cumulative rank (NCR) values, which quantifies the SN association to HII regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities at higher metallicities. The luminosity increment in the optical bands during SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM quiescent optical luminosities tend to be lower. The difference in metallicity between SNe IIn and SN IMs indicates that LBVs are only one of the progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly arising from LBVs and RSGs, respectively. Finally, even though line-driven winds likely do not primarily drive the late mass-loss of CSI SN progenitors, metallicity has some impact on the observational properties of these transients.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/22
- Title:
- CIV broad abs. line SDSS QSO obs. with Gemini
- Short Name:
- J/ApJ/862/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We isolate a set of quasars that exhibit emergent CIV broad absorption lines (BALs) in their spectra by comparing spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 and the SDSS/BOSS Data Releases 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. We find an emergence rate consistent with the previously reported disappearance rate of BAL quasars given the relative numbers of non-BAL and BAL quasars in the SDSS. We find that candidate newly emerged BALs are preferentially drawn from among BALs with smaller balnicity indices, shallower depths, larger velocities, and smaller widths. Within two rest-frame years (average) after a BAL has emerged, we find it equally likely to continue increasing in equivalent width in an observation 6 months later (average) as it is to start decreasing. From the time separations between our observations, we conclude that the coherence timescale of BALs is less than 100 rest-frame days. We observe coordinated variability among pairs of troughs in the same quasar, likely due to clouds at different velocities responding to the same changes in ionizing flux, and the coordination is stronger if the velocity separation between the two troughs is smaller. We speculate that the latter effect may be due to clouds having on average lower densities at higher velocities owing to mass conservation in an accelerating flow, causing the absorbing gas in those clouds to respond on different timescales to the same ionizing flux variations.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/23
- Title:
- CIV NAL systems from SDSS-DR14 quasar spectra
- Short Name:
- J/ApJS/239/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for CIV{lambda}{lambda}1548,1551 narrow absorption doublets in spectral data from the blue wing {upsilon}r=30000km/s until the red wing of CIV{lambda}1549 emission lines. We have obtained 21239 CIV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from {Delta}MJD=0.24 to 1842.38 days at rest-frame. Both samples of the C IV NAL systems with multi-epoch observations and the variable C IV NAL systems are the largest ones to date. The offset velocity distribution of the variable C IV NALs from quasars has a peak at {upsilon}r~2000km/s and gently extends to a larger offset velocity. There are 110 variable C IV NALs with {upsilon}r>12000km/s. In addition, about 10% intrinsic C IV NALs show time variability on a timescale of <2000 days. We find that the variations of C IV NALs are positively or negatively correlated with the alternations of quasar continua. The two kinds of correlations suggest that the variable C IV NALs included in our absorber catalog can be classified into at least two populations: (1) highly ionized systems that are dominated by highly ionized absorbing gas and negatively respond to the fluctuations of quasar emissions; and (2) lowly ionized systems that are dominated by lowly ionized absorbing gas and positively respond to fluctuations of quasar emissions. We also find that the absolute fractional changes in the absorption strengths of C IV NALs are inversely correlated with absorption strengths.
