- ID:
- ivo://CDS.VizieR/J/A+A/623/A25
- Title:
- Photometric and astrometric study of NGC 6530
- Short Name:
- J/A+A/623/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6530 is a young cluster, with a complex morphology and star-formation history. We present a statistical study of its global properties, using a new, large list of candidate members down to masses of 0.2-0.4M_{sun}_ and Gaia DR2 astrometry. We consider a larger sky region compared to previous studies, to investigate the entire cluster until its periphery, including any diffuse population all around the main cluster. We study the distribution of extinction and age across the different regions, and obtain constraints on the star-formation history. We also study the dynamics of cluster members. Cluster membership was determined on the basis of literature X-ray data, H{alpha} emission, near-IR and UV excesses from the VPHAS+ and UKIDSS photometric surveys and published near-IR catalogs, and Gaia DR2 astrometry; moreover, we used a method for photometric selection of M-type pre-main-sequence cluster members, which we recently developed and used for other star-formation regions. The list of candidates includes nearly 3700 stars, of which we estimate approximately 2700 to be genuine NGC 6530 members. Using Gaia parallaxes, the cluster distance is found to be 1325pc, with errors of 0.5% (statistical) and 8.5% (systematic), in agreement with previous determinations. The cluster morphology and boundaries are established with great confidence, from the agreement between the subsamples of members selected using different criteria. There is no diffuse population of members around the cluster, but there are minor condensations of true members in addition to the two main groups in the cluster core and in the Hourglass nebula. Two such subgroups are spatially associated with the stars 7 Sgr (F2II-III) and HD 164536 (O7.5V). There is a definite pattern of sequential star formation across the cluster, within an age range from less than 0.5Myr to ~5Myr. Extinction is spatially non-uniform, with part of the population still embedded or obscured by thick dust. The precise Gaia proper motion data indicate that the NGC 6530 parent cloud collided with the Galactic plane around 4Myr ago, and we suggest that event as the trigger of the bulk of star formation in NGC 6530. The internal cluster dynamics is also partially resolved by the Gaia data, indicating expansion of the main cluster population with respect to its center.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/742/61
- Title:
- Photometric redshift of AGNs from XMM- and C-COSMOS
- Short Name:
- J/ApJ/742/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy {sigma}_{Delta}z_/(1+z_spec_)~0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2deg^2^ of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by {Delta}z>0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H_AB_=24mag).
- ID:
- ivo://CDS.VizieR/J/ApJS/187/560
- Title:
- Photometric redshifts of the 2Ms CDF-S
- Short Name:
- J/ApJS/187/560
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present reliable multiwavelength identifications and high-quality photometric redshifts for the 462 X-ray sources in the ~2Ms Chandra Deep Field-South (CDF-S) survey (Cat. J/ApJS/179/19). Source identifications are carried out using deep optical-to-radio multiwavelength catalogs, and are then combined to create lists of primary and secondary counterparts for the X-ray sources. We identified reliable counterparts for 442 (95.7%) of the X-ray sources, with an expected false-match probability of ~6.2%; we also selected four additional likely counterparts. The majority of the other 16 X-ray sources appear to be off-nuclear sources, sources associated with galaxy groups and clusters, high-redshift active galactic nuclei (AGNs), or spurious X-ray sources. A likelihood-ratio method is used for source matching, which effectively reduces the false-match probability at faint magnitudes compared to a simple error-circle matching method. We construct a master photometric catalog for the identified X-ray sources including up to 42 bands of UV-to-infrared data, and then calculate their photometric redshifts (photo-z's). The typical photo-z accuracy is ~6%-7%.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/73
- Title:
- Photometric redshifts of X-ray sources in CDF-S
- Short Name:
- J/ApJS/155/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the photometry of 10 near-ultraviolet, optical, and near-infrared bands of the Chandra Deep Field-South, we estimate the photometric redshifts for 342 X-ray sources, which constitute ~99% of all the detected X-ray sources in the field.
- ID:
- ivo://CDS.VizieR/J/ApJS/218/20
- Title:
- Photometric variability search in the CSTAR field
- Short Name:
- J/ApJS/218/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Chinese Small Telescope Array (CSTAR) is the first telescope facility built at Dome A, Antarctica. During the 2008 observing season, the installation provided long-baseline and high-cadence photometric observations in the i-band for 18145 targets within 20deg^2^ CSTAR field around the South Celestial Pole for the purpose of monitoring the astronomical observing quality of Dome A and detecting various types of photometric variability. Using sensitive and robust detection methods, we discover 274 potential variables from this data set, 83 of which are new discoveries. We characterize most of them, providing the periods, amplitudes, and classes of variability.
- ID:
- ivo://CDS.VizieR/J/A+A/389/439
- Title:
- Photometry in field of RX J004404.8+411820
- Short Name:
- J/A+A/389/439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We propose the first association of an optical counterpart with a luminous supersoft X-ray source in M31, RX J0044.0+4118, observed with ROSAT in July 1991. The PSPC position is at 1.644 angular distance from a candidate nova in outburst in September of 1990. This is interesting because the incidence of classical novae among supersoft X-ray sources is an open question. The proposed optical counterpart was measured at R~=17.7 in September of 1990, and it had faded to R>19.2 when it was observed again after 70 days. The light curve was too sparsely monitored for definite conclusions on the speed class of the nova. No other variable objects with V<23.5 were found in the ROSAT spatial error box. We evaluate that the probability that a classical or recurrent nova was in outburst in the ROSAT error box in the few years preceding the observation is very small, so the proposed identification is meaningful. We also show evidence that the associated supersoft X-ray source turned off in the third year after the outburst.
- ID:
- ivo://CDS.VizieR/J/ApJ/721/412
- Title:
- Photometry of polar CV* 1RXS J173006.4+033813
- Short Name:
- J/ApJ/721/412
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of 1RXS J173006.4+033813, a polar cataclysmic variable with a period of 120.21 minutes. The white dwarf primary has a magnetic field of B=42^+6^_-5_MG and the secondary is an M3 dwarf. The system shows highly symmetric double-peaked photometric modulation in the active state as well as in quiescence. These arise from a combination of cyclotron beaming and ellipsoidal modulation. The projected orbital velocity of the secondary is K_2_=390+/-4km/s. We place an upper limit of 830+/-65pc on the distance.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A119
- Title:
- Pismis 24 stars with X-ray emission
- Short Name:
- J/A+A/539/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Circumstellar disks are expected to evolve quickly in massive young clusters harboring many OB-type stars. Two processes have been proposed to drive the disk evolution in such cruel environments: (1) gravitational interaction between circumstellar disks and nearby passing stars (stellar encounters), and (2) photoevaporation by UV photons from massive stars. The relative importance of both mechanisms is not well understood. Studies of massive young star clusters can provide observational constraints on the processes of driving disk evolution. We investigate the properties of young stars and their disks in the NGC 6357 complex, concentrating on the most massive star cluster within the complex: Pismis 24.
- ID:
- ivo://CDS.VizieR/J/A+A/541/A160
- Title:
- Planck + X/{gamma} observations of blazars
- Short Name:
- J/A+A/541/A160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and {gamma}-ray bands, with additional 5GHz flux-density limits to ensure a good probability of a Planck detection. We compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set allows us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A4
- Title:
- PLCK G004.5-19.5 images at 150, 325 and 610MHz
- Short Name:
- J/A+A/607/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radio observations of the galaxy cluster PLCK G004.5-19.5 (z=0.52) using the Giant Metrewave Radio Telescope at 150MHz, 325MHz, and 610MHz. We find an unusual arrangement of diffuse radio emission in the center and periphery of the cluster, as well as several radio galaxies with head-tail emission. A patch of peripheral emission resembles a radio relic, and central emission resembles a radio halo. Reanalysis of archival XMM-Newton X-ray data shows that PLCK G004.5-19.5 is disturbed, which has a known correlation with the existence of radio relics and halos. Given that the number of known radio halos and radio relics at z>0.5 is very limited, PLCK G004.5-19.5 is an important addition to understanding merger-related particle acceleration at higher redshifts.
