- ID:
- ivo://CDS.VizieR/J/ApJS/160/511
- Title:
- Orion Nebula Cluster proplyd candidates
- Short Name:
- J/ApJS/160/511
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the X-ray and near-infrared emission properties of a sample of pre-main-sequence (PMS) stellar systems in the Orion Nebula Cluster (ONC) that display evidence for circumstellar disks ("proplyds") and optical jets in Hubble Space Telescope (HST) imaging. Our study uses X-ray data acquired during Chandra Orion Ultradeep Program (COUP) observations, as well as complementary optical and near-infrared data recently acquired with HST and the Very Large Telescope (VLT), respectively.
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- ID:
- ivo://CDS.VizieR/J/A+A/299/39
- Title:
- Orion Trapezium area ROSAT PSPC obs. I.
- Short Name:
- J/A+A/299/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep ROSAT PSPC image centred on the Orion Trapezium has revealed that most of the X-ray emission originates from discrete sources, in contrast to previous EINSTEIN data which suggested a diffuse emission component. We present a list of 171 X-ray sources all situated in the so-called inner ring of the field of view (20' radius). The field is crowded with sources. A special procedure had to be developed to cope with the severe blending of sources. The present list is not complete for L_X_<3.5*10^29^erg/s due to this reason and many more sources can still be expected by a next step in the reduction. Nearly all of the sources could be identified with pre-main sequence stars of the Ori OB 1 association in its subgroups Ic and Id. The statistics of this ensemble are discussed. It seems that members of the above subgroups can be distinguished on the basis of an additional amount of X-ray extinction seen in their spectra or hardness ratios. The O stars in the area ({teta}1 Ori C, {teta}2 Ori A and {iota} Ori) are briefly discussed. Six B stars are identified with X-ray sources.
- ID:
- ivo://CDS.VizieR/J/AN/321/81
- Title:
- Orion Trapezium area ROSAT PSPC obs. II.
- Short Name:
- J/AN/321/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep ROSAT PSPC image centred on the Orion Trapezium has been reduced a second time using an improved version of the PSF to fit the data. The outer rim of the field of view was also included. The new catalogue contains 316 X-ray sources which are easily identified with pre-main sequence stars of the Ori OB1 Ic and Id association. All 316 sources were tested for variability. No variations were found inside the single exposures of about 45 minutes length each. Between the 4 exposures spaced over 5 days about 1/3 of the sources show signs of activities of various forms. As above 25% of these have somewhat regular lights curves (monotonically rising or falling or hill- shaped) we infer that at least some outbursts with time scales longer than a day are present and that past searches for X-ray flares of pre-main sequence stars were biased towards shorter time scales.
- ID:
- ivo://CDS.VizieR/J/A+A/510/A48
- Title:
- Palermo Swift-BAT Hard X-ray Catalogue
- Short Name:
- J/A+A/510/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Palermo Swift-BAT hard X-ray catalogue obtained from the analysis of the the data relative to the first 39 months of the Swift mission. We have developed a dedicated software to perform data reduction, mosaicking and source detection on the BAT survey data. We analyzed the BAT dataset in three energy bands (14-150keV, 14-30keV, 14-70keV), obtaining a list of 962 detections above a significance threshold of 4.8 standard deviations. The identification of the source counterparts was pursued using three strategies: cross-correlation with published hard X-ray catalogues, analysis of field observations of soft X-ray instruments, cross-correlation with the SIMBAD database. The survey covers 90% of the sky down to a flux limit of 2.5x10^-11^erg/cm^2^/s and 50% of the sky down to a flux limit of 1.8x10^-11^erg/cm^2^/s in the 14-150keV band. We derived a catalogue of 754 identified sources, of which ~69% are extragalactic, ~27% are Galactic objects, ~4% are already known X-ray or gamma ray emitters whose nature has not been determined yet. The integrated flux of the extragalactic sample is ~1% of the Cosmic X-ray background in the 14-150keV range.
- 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.
- 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/ApJ/903/31
- Title:
- Photometry AT 2018hyz with Swift XRT, UVOT and Swope
- Short Name:
- J/ApJ/903/31
- Date:
- 11 Mar 2022 14:12:05
- Publisher:
- CDS
- Description:
- We present the multiwavelength analysis of the tidal disruption event (TDE) AT2018hyz (ASASSN-18zj). From follow-up optical spectroscopy, we detect the first unambiguous case of resolved double-peaked Balmer emission in a TDE. The distinct line profile can be well-modeled by a low eccentricity (e~0.1) accretion disk extending out to ~100Rp and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out. Our analysis indicates that in AT2018hyz, disk formation took place promptly after the most-bound debris returned to pericenter, which we estimate to be roughly tens of days before the first detection. Redistribution of angular momentum and mass transport, possibly through shocks, must occur on the observed timescale of about a month to create the large H{alpha}-emitting disk that comprises <~5% of the initial stellar mass. With these new insights from AT2018hyz, we infer that circularization is efficient in at least some, if not all optically bright, X-ray faint TDEs. In these efficiently circularized TDEs, the detection of double-peaked emission depends on the disk inclination angle and the relative strength of the disk contribution to the non-disk component, possibly explaining the diversity seen in the current sample.