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4331. New young stars and brown dwarfs in Upper Sco
ID:
ivo://CDS.VizieR/J/AJ/156/76
Title:
New young stars and brown dwarfs in Upper Sco
Short Name:
J/AJ/156/76
Date:
21 Oct 2021
Publisher:
CDS
Description:
To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our new compilation of all known members of the association contains 1631 objects. Although the census of Upper Sco has expanded significantly over the last decade, there remain hundreds of candidates that lack spectroscopy. The precise parallaxes and proper motions from the second data release of Gaia should extend down to substellar masses in Upper Sco, which will greatly facilitate the identification of the undiscovered members.
4332. New young stellar cluster towards IRAS 04186+5143
ID:
ivo://CDS.VizieR/J/MNRAS/452/1523
Title:
New young stellar cluster towards IRAS 04186+5143
Short Name:
J/MNRAS/452/1523
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the discovery of a new young stellar cluster in the outer Galaxy located at the position of an IRAS Point Source Catalog source that has been previously misidentified as an external galaxy. The cluster is seen in our near-infrared imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the young stellar nature of the sources detected. There is also evidence of subclustering seen in the spatial distributions of young stars and of gas and dust. Near- and mid-infrared photometry indicates that the stars exhibit colours compatible with reddening by interstellar and circumstellar dust and are likely to be low- and intermediate-mass young stellar objects (YSOs) with a large proportion of Class I YSOs. Ammonia and CO lines were detected, with the CO emission well centred near the position of the richest part of the cluster. The velocity of the CO and NH3 lines indicates that the gas is Galactic and located at a distance of about 5.5kpc, in the outer Galaxy. Herschel data of this region characterize the dust environment of this molecular cloud core where the young cluster is embedded. We derive masses, luminosities, and temperatures of the molecular clumps where the young stars reside and discuss their evolutionary stages.
4333. New z>=3.6 QSOs from FIRST-SDSS DR5
ID:
ivo://CDS.VizieR/J/MNRAS/391/369
Title:
New z>=3.6 QSOs from FIRST-SDSS DR5
Short Name:
J/MNRAS/391/369
Date:
21 Oct 2021
Publisher:
CDS
Description:
We aim to obtain a complete sample of redshift z>=3.6 radio quasi-stellar objects (QSOs) from the Faint Images of the Radio Sky at Twenty cm survey (FIRST) sources (S_1.4GHz_>1mJy) having star-like counterparts in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) photometric survey (r_AB_<=20.2). Our starting sample of 8665 FIRST-DR5 pairs includes 4250 objects with spectra in DR5, 52 of these being z>=3.6 QSOs. We found that simple supervised neural networks, trained on the sources with DR5 spectra, and using optical photometry and radio data, are very effective for identifying high-z QSOs in a sample without spectra. For the sources with DR5 spectra the technique yields a completeness (fraction of actual high-z QSOs classified as such by the neural network) of 96 per cent, and an efficiency (fraction of objects selected by the neural network as high-z QSOs that actually are high-z QSOs) of 62 per cent. Applying the trained networks to the 4415 sources without DR5 spectra we found 58 z>=3.6 QSO candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z QSOs. Spectra of 13 additional candidates from the literature and from SDSS Data Release 6 (DR6) revealed seven more z>=3.6 QSOs, giving an overall efficiency of 60 per cent (24/40).
4334. New 2.2<z<3.5 quasars from SDSS and UKIDSS
ID:
ivo://CDS.VizieR/J/AJ/146/100
Title:
New 2.2<z<3.5 quasars from SDSS and UKIDSS
Short Name:
J/AJ/146/100
Date:
21 Oct 2021
Publisher:
CDS
Description:
The identification of quasars at intermediate redshifts (2.2<z<3.5) has been inefficient in most previous quasar surveys since the optical colors of quasars are similar to those of stars. The near-IR K-band excess technique has been suggested to overcome this difficulty. Our recent study also proposed to use optical/near-IR colors for selecting z<4 quasars. To verify the effectiveness of this method, we selected a list of 105 unidentified bright targets with i<=18.5 from the quasar candidates of SDSS DR6 with both SDSS ugriz optical and UKIDSS YJHK near-IR photometric data, which satisfy our proposed Y-K/g-z criterion and have photometric redshifts between 2.2 and 3.5 estimated from the nine-band SDSS-UKIDSS data. We observed 43 targets with the BFOSC instrument on the 2.16m optical telescope at Xinglong station of the National Astronomical Observatory of China in the spring of 2012. We spectroscopically identified 36 targets as quasars with redshifts between 2.1 and 3.4. The high success rate of discovering these quasars in the SDSS spectroscopic surveyed area further demonstrates the robustness of both the Y-K/g-z selection criterion and the photometric redshift estimation technique. We also used the above criterion to investigate the possible stellar contamination rate among the quasar candidates of SDSS DR6, and found that the rate is much higher when selecting 3<z<3.5 quasar candidates than when selecting lower redshift candidates (z<2.2). The significant improvement in the photometric redshift estimation when using the nine-band SDSS-UKIDSS data over the five-band SDSS data is demonstrated and a catalog of 7727 unidentified quasar candidates in SDSS DR6 selected with optical/near-IR colors and having photometric redshifts between 2.2 and 3.5 is provided. We also tested the Y-K/g-z selection criterion with the recently released SDSS-III/DR9 quasar catalog and found that 96.2% of 17999 DR9 quasars with UKIDSS Y- and K-band data satisfy our criterion. With some available samples of red quasars and type II quasars, we find that 88% and 96.5% of these objects can be selected by the Y-K/g-z criterion, respectively, which supports our claim that using the Y-K/g-z criterion efficiently selects both unobscured and obscured quasars. We discuss the implications of our results on the ongoing and upcoming large optical and near-IR sky surveys.
4335. New 2.2<z<3 quasars from SDSS and UKIDSS
ID:
ivo://CDS.VizieR/J/AJ/142/78
Title:
New 2.2<z<3 quasars from SDSS and UKIDSS
Short Name:
J/AJ/142/78
Date:
21 Oct 2021
Publisher:
CDS
Description:
The identification of quasars in the redshift range 2.2<z<3 is known to be very inefficient because the optical colors of such quasars are indistinguishable from those of stars. Recent studies have proposed using optical variability or near-infrared (near-IR) colors to improve the identification of the missing quasars in this redshift range. Here we present a case study combining both methods. We select a sample of 70 quasar candidates from variables in Sloan Digital Sky Survey (SDSS) Stripe 82, which are non-ultraviolet excess sources and have UKIDSS near-IR public data. They are clearly separated into two parts on the Y-K/g-z color-color diagram, and 59 of them meet or lie close to a newly proposed Y-K/g-z selection criterion for z<4 quasars. Of these 59 sources, 44 were previously identified as quasars in SDSS DR7, and 35 of them are quasars at 2.2<z<3. We present spectroscopic observations of 14 of 15 remaining quasar candidates using the Bok 2.3m telescope and the MMT 6.5m telescope, and successfully identify all of them as new quasars at z=2.36-2.88. We also apply this method to a sample of 643 variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected from 1875 new quasar candidates in SDSS Stripe 82 given by Butler & Bloom (2011AJ....141...93B) based on the time-series selections, and find that 188 of them are probably new quasars with photometric redshifts at 2.2<z<3. Our results indicate that the combination of optical variability and optical/near-IR colors is probably the most efficient way to find 2.2<z<3 quasars and is very helpful for constructing a complete quasar sample. We discuss its implications for ongoing and upcoming large optical and near-IR sky surveys.
4336. Next Generation Fornax Survey (NGFS) II.
ID:
ivo://CDS.VizieR/J/ApJ/855/142
Title:
Next Generation Fornax Survey (NGFS) II.
Short Name:
J/ApJ/855/142
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a photometric study of the dwarf galaxy population in the core region (<~r_vir_/4) of the Fornax galaxy cluster based on deep u'g'i' photometry from the Next Generation Fornax Cluster Survey. All imaging data were obtained with the Dark Energy Camera mounted on the 4m Blanco telescope at the Cerro Tololo Interamerican Observatory. We identify 258 dwarf galaxy candidates with luminosities -17<~Mg'<~-8mag, corresponding to typical stellar masses of 9.5>~logM*/M_{sun}_>~5.5, reaching ~3mag deeper in point-source luminosity and ~4mag deeper in surface brightness sensitivity compared to the classic Fornax Cluster Catalog. Morphological analysis shows that the dwarf galaxy surface-brightness profiles are well represented by single-component Sersic models with average Sersic indices of <n>_u',g',i'_=(0.78-0.83)+/-0.02 and average effective radii of <r_e_>_u',g',i'_=(0.67-0.70+/-0.02kpc. Color-magnitude relations indicate a flattening of the galaxy red sequence at faint galaxy luminosities, similar to the one recently discovered in the Virgo cluster. A comparison with population synthesis models and the galaxy mass-metallicity relation reveals that the average faint dwarf galaxy is likely older than ~5Gyr. We study galaxy scaling relations between stellar mass, effective radius, and stellar mass surface density over a stellar mass range covering six orders of magnitude. We find that over the sampled stellar mass range several distinct mechanisms of galaxy mass assembly can be identified: (1) dwarf galaxies assemble mass inside the half-mass radius up to logM*~8.0, (2) isometric mass assembly occurs in the range 8.0<~logM*/M_{sun}_<~10.5, and (3) massive galaxies assemble stellar mass predominantly in their halos at logM*~10.5 and above.
4337. NGC 6440
ID:
ivo://CDS.VizieR/J/A+AS/108/653
Title:
NGC 6440
Short Name:
J/A+AS/108/653
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
4338. NGC 2004
ID:
ivo://CDS.VizieR/J/AJ/102/137
Title:
NGC 2004
Short Name:
J/AJ/102/137
Date:
21 Oct 2021
Publisher:
CDS
Description:
The results of a new CCD photometric investigation of stars in the field of the LMC cluster NGC 2004 are reported and discussed. B, V photometry is given for more than 1500 objects, the large majority to be ascribed to the cluster. A new color-magnitude diagram is presented. It shows a well-defined blue sequence (BS) of H-burning stars, running from V~=21mag up to V~=13mag, together with a group of cluster He-burning red supergiants with V~=13mag and a clump of field red giants at about V~=19 mag. Theoretical evolutionary computations are reported covering the range of massive stars evolving in the cluster. These evolutionary tracks can match the observed CM diagram provided that a low efficiency of the surface convection (a low value of the mixing length) is adopted. Comparison of the theoretical luminosity function with the upper portion of the observed BS distribution suggests a cluster age of about 8 million years, in agreement with previous evaluations. The completeness of the sample and the contribution of field stars have been estimated. The CM distribution of cluster stars has been compared with the results of synthetic clusters based on the adopted evolutionary scenario. We find that the observed distribution of cluster stars in the different evolutionary phases appears in good agreement with prediction based on theoretical evolutionary lifetimes. Moreover, the distribution of H-burning stars agrees with a Salpeter distribution in the whole range 2<=M/M_{sun}_<=20. After a short review of the current theoretical scenario concerning massive stars, the CM diagram of field stars is discussed, reaching the conclusion that the observed clump of red giants is the natural consequence of the peculiar large lifetimes in the central He burning phase of stars with M~=3M_{sun}_.
4339. NGC 6340
ID:
ivo://CDS.VizieR/J/A+A/504/389
Title:
NGC 6340
Short Name:
J/A+A/504/389
Date:
21 Oct 2021
Publisher:
CDS
Description:
Lenticular galaxies are believed to form by a combination of environmental effects and secular evolution. We study the nearby disc-dominated S0 galaxy NGC 6340 photometrically and spectroscopically to understand the mechanisms of S0 formation and evolution in groups. ************************************************************************** * * * Sorry, but the author(s) never supplied the tabular material * * announced in the paper * * * **************************************************************************
4340. NGC 6584
ID:
ivo://CDS.VizieR/J/AJ/109/1112
Title:
NGC 6584
Short Name:
J/AJ/109/1112
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present CCD photometry in the B and V passbands for the Galactic globular cluster NGC 6584. The color-magnitude diagram reveals a horizontal branch (HB) populated on both the red and blue sides of the RR Lyrae instability strip. The cluster contains 42 confirmed RR Lyrae variables, and we find an additional 56 stars which are possible RR Lyraes. The mean magnitude of the RR Lyraes on our CCD frames is combined with that of the nonvariable stars to yield <V(HB)> = 16.53 +/- 0.03. Using a polynomial fit to the cluster giant stars, we derive the color of the giant branch at the level of the HB to be (B-V)g = 0.89 +/- 0.02. Our photometry has also been used to isolate the red giant branch "clump," which forms when stars pause and sometimes reverse their course as they evolve up the giant branch. Its luminosity is primarily dependent upon the cluster metallicity, and we have used this fact to derive a metallicity of [Fe/H] = -1.44 +/- 0.16 for NGC 6584. Coupled with the color of the giant branch given above, this yields a cluster reddening of E(B-V) = 0.07 +/- 0.04. To the extent that our photometry can be used to study the age of NGC 6584, we find it to be comparable to M3, which is not surprising given their similar HB morphologies. The color-magnitude diagram also exhibits a significant population of blue straggler stars. From a comparison of the blue straggler radial distribution to that of the subgiant stars with similar V magnitudes, we find that the blue stragglers are more centrally concentrated than the subgiants, indicative of a higher mass for the blue stragglers.