- ID:
- ivo://CDS.VizieR/J/AJ/128/1233
- Title:
- LkH{alpha} 101 and the young cluster in NGC 1579
- Short Name:
- J/AJ/128/1233
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The central region of the dark cloud L1482 is illuminated by LkH{alpha} 101, a heavily reddened (A_V_~10mag) high-luminosity (>=8x10^3^L_Sun_) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R=16 and >21) H{alpha} emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700pc. Radio observations suggest that the optical object LkH{alpha} 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell.
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- ID:
- ivo://CDS.VizieR/J/AJ/160/49
- Title:
- LOAO BV-bands photometry and BOES RVs of WASP 0131+28
- Short Name:
- J/AJ/160/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first BV light curves and high-resolution spectra of the post-mass transfer binary star WASP0131+28 to study the absolute properties of extremely low-mass white dwarfs. From the observed spectra, the double-lined radial velocities were derived, and the effective temperature and rotational velocity of the brighter, more massive primary were found to be Teff_1_=10000{+/-]200K and v_1_sin_i_=55{+/-}10km/s, respectively. The combined analysis of the Transiting Exoplanet Survey Satellite (TESS) archive data and ours yielded the accurate fundamental parameters of the program target. The masses were derived to about 1.0% accuracy and the radii to 0.6%, or better. The secondary component's parameters of M_2_=0.200{+/-}0.002M_{sun}_, R_2_=0.528{+/-}0.003R_{sun}_, Teff_2_=11186{+/-}235K, and L_2_=3.9{+/-}0.3L_{sun}_ are in excellent agreement with the evolutionary sequence for a helium-core white dwarf of mass 0.203M_{sun}, and indicates that this star is halfway through the constant luminosity phase. The results presented in this article demonstrate that WASP0131+28 is an EL CVn eclipsing binary in a thin disk, which is formed from the stable Roche-lobe overflow channel and composed of a main-sequence dwarf with a spectral type A0 and a pre-He white dwarf.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/25
- Title:
- Long-term optical monitoring of E1821+643
- Short Name:
- J/ApJS/222/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of the first long-term (1990-2014) optical spectrophotometric monitoring of a binary black hole candidate QSO E1821+643, a low-redshift, high-luminosity, radio-quiet quasar. In the monitored period, the continua and H{gamma} fluxes changed about two times, while the H{beta} flux changed about 1.4 times. We found periodical variations in the photometric flux with periods of 1200, 1850, and 4000 days, and 4500-day periodicity in the spectroscopic variations. However, the periodicity of 4000-4500 days covers only one cycle of variation and should be confirmed with a longer monitoring campaign. There is an indication of the period around 1300 days in the spectroscopic light curves, but with small significance level, while the 1850-day period could not be clearly identified in the spectroscopic light curves. The line profiles have not significantly changed, showing an important red asymmetry and broad line peak redshifted around +1000km/s. However, H{beta} shows a broader mean profile and has a larger time lag ({tau}~120 days) than H{gamma} ({tau}~60 days). We estimate that the mass of the black hole is ~2.6x10^9^M_{sun}_. The obtained results are discussed in the frame of the binary black hole hypothesis. To explain the periodicity in the flux variability and high redshift of the broad lines, we discuss a scenario where dense, gas-rich, cloudy-like structures are orbiting around a recoiling black hole.
- ID:
- ivo://CDS.VizieR/J/ApJ/823/157
- Title:
- LOS velocities & [Fe/H] of Pal 5 tidal stream
- Short Name:
- J/ApJ/823/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Subaru/Faint Object Camera and Spectrograph and Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectroscopy of a tidally disrupting Milky Way (MW) globular cluster Palomar 5 (Pal 5) and its tidal stream. The observed fields are located to cover an angular extent of ~17{deg} along the stream, providing an opportunity to investigate a trend in line-of-sight velocities (V_los_) along the stream, which is essential to constrain its orbit and underlying gravitational potential of the MW's dark matter halo. A spectral fitting technique is applied to the observed spectra to obtain stellar parameters and metallicities ([Fe/H]) of the target stars. The 19 stars most likely belonging to the central Pal 5 cluster have a mean V_los_ of -58.1+/-0.7km/s and metallicity [Fe/H]=-1.35+/-0.06dex, both of which are in good agreement with those derived in previous high-resolution spectroscopic studies. Assuming that the stream stars have the same [Fe/H] as the progenitor cluster, the derived [Fe/H] and V_los_ values are used to estimate the possible V_los_ range of the member stars at each location along the stream. Because of the heavy contamination of the field MW stars, the estimated V_los_ range depends on prior assumptions about the stream's V_los_, which highlights the importance of more definitely identifying the member stars using proper motion and chemical abundances to obtain unbiased information of V_los_ in the outer part of the Pal 5 stream. The models for the gravitational potential of the MW's dark matter halo that are compatible with the estimated V_los_ range are discussed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/997
- Title:
- Low-luminosity radio-loud AGN
- Short Name:
- J/MNRAS/465/997
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HI absorption studies of active galaxies enable us to probe their circumnuclear regions and the general interstellar medium and study the supply of gas that may trigger nuclear activity. In this article, we investigate the dependence of the detection rate of HI absorption on the nature of radio galaxies based on their emission-line spectra and on the nature of host galaxies based on WISE colours and their radio structure, which may help us understand the different accretion modes. We find significant differences in the distributions of W2-W3 colour for sources with HI absorption detections and non-detections. We report a high detection rate of HI absorption in those galaxies with WISE infrared colours W2-W3>2, typical of gas-rich systems, along with a compact radio structure. The HI detection rate for low-excitation radio galaxies (LERGs) with W2-W3>2 and compact radio structure is high (70.6+/-20.4 per cent). In high-excitation radio galaxies (HERGs), compact radio structure in the nuclear or circumnuclear region could give rise to absorption by gas in the dusty torus, in addition to gas in the interstellar medium. However, the higher specific star-formation rate (sSFR) for LERGs with W2-W3>2 suggests that HI absorption may be largely due to star-forming gas in their hosts. LERGs with extended radio structure tend to have significantly lower values of W2-W3 compared with those with compact structure. Extended radio sources and those with W2-W3<2 have low HI detection rates.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/167
- Title:
- Low-mass black holes in SDSS Seyfert 1 galaxies
- Short Name:
- J/ApJ/755/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad H{alpha} emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN-galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range 8x10^4^-2x10^6^M_{sun}_ (with a median of 1.2x10^6^M_{sun}_), using the virial mass estimator based on the broad H{alpha} line. About half of our sample of low-mass BHs differs from that of Greene & Ho (2007, Cat. J/ApJ/670/92), with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from <~0.01 to ~1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of L* field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1Gyr.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/40
- Title:
- Low-mass black holes in Sy1 galaxies. II. SDSS-DR7
- Short Name:
- J/ApJS/235/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of (1-20)x10^5^M_{sun}_. The AGNs are selected through a systematic search among galaxies in the Seventh Data Release (DR7) of the Sloan Digital Sky Survey (SDSS), and careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from SDSS DR4 makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the [OIII] luminosity. The effective optical-to-X-ray spectral indices {alpha}_OX_, albeit with a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity L_2500{AA}_. Interestingly, a correlation of {alpha}_OX_ with black hole mass is also found, with {alpha}OX being statistically flatter (stronger X-ray relative to optical) for lower black hole masses. Only 26 objects, mostly radio loud, were detected in radio at 20cm in the FIRST survey, giving a radio-loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of 10^8.8^-10^12.4^M_{sun}_ and optical colors typical of Sbc spirals. They are dominated by young stellar populations that seem to have undergone continuous star formation history.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/654
- Title:
- Low-mass members of Chamaeleon I
- Short Name:
- J/ApJ/684/654
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used images obtained with the Infrared Array Camera and the Multiband Imaging Photometer on board the Spitzer Space Telescope to search for low-mass stars and brown dwarfs with circumstellar disks in the Chamaeleon I star-forming region. Through optical spectroscopy of sources with red colors in these data, we have identified seven new disk-bearing members of the cluster. Three of these objects are probably brown dwarfs, according to their spectral types (M8, M8.5, M8-L0). Three of the other new members may have edge-on disks, based on the shapes of their infrared spectral energy distributions. One of the possible edge-on systems has a steeply rising slope from 4.5 to 24um, indicating that it could be a Class I source (star+disk+envelope) rather than a Class II source (star+disk). If so, then it would be one of the least massive known Class I protostars (M5.75, M~0.1M_{sun}_).
- ID:
- ivo://CDS.VizieR/J/AJ/154/14
- Title:
- Low-mass stars in 25 Ori group and Orion OB1a
- Short Name:
- J/AJ/154/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion OB1a sub-association is a rich low-mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent overdensity of Orion OB1a. Nonetheless, the current census of the 25 Ori members is estimated to be lower than 50% complete, leaving a large number of members to be still confirmed. We retrieved 172 low-resolution stellar spectra in Orion OB1a observed as ancillary science in the SDSS-III/BOSS survey, for which we classified their spectral types and determined physical parameters. To determine memberships, we analyzed the H{alpha} emission, LiI{lambda}6708 absorption, and NaI{lambda}{lambda}8183,8195 absorption as youth indicators in stars classified as M type. We report 50 new LMSs spread across the 25 Orionis, ASCC18, and ASCC20 stellar groups with spectral types from M0 to M6, corresponding to a mass range of 0.10{<=}m/M_{Sun}_{<=}0.58. This represents an increase of 50% in the number of known LMSs in the area and a net increase of 20% in the number of 25 Ori members in this mass range. Using parallax values from the Gaia DR1 catalog, we estimated the distances to these three stellar groups and found that they are all co-distant, at 338+/-66pc. We analyzed the spectral energy distributions of these LMSs and classified their disks into evolutionary classes. Using H-R diagrams, we found a suggestion that 25 Ori could be slightly older than the other two observed groups in Orion OB1a.
- ID:
- ivo://CDS.VizieR/J/A+A/488/167
- Title:
- Low-mass stars in {sigma} Ori and {lambda} Ori
- Short Name:
- J/A+A/488/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10Myr) clusters {sigma} Ori and {lambda} Ori. We observed 98 and 49 low-mass (0.2-1.0M_{sun}_stars in {sigma} Ori and {lambda} Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R~17000) HR15N grating (6470-6790{AA}). We used radial velocities, Li and H{alpha} to establish cluster membership and H{alpha} and other optical emission lines to analyze the accretion properties of members. We identified 65 and 45 members of the {sigma} Ori and {lambda} Ori clusters, respectively, and discovered 16 new candidate binary systems.