- ID:
- ivo://CDS.VizieR/J/AJ/134/999
- Title:
- X-ray observations of NGC 2264
- Short Name:
- J/AJ/134/999
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an X-ray imaging survey of the young cluster NGC 2264, carried out with the European Photon Imaging Cameras (EPIC) on board the XMM-Newton spacecraft. The X-ray data are merged with extant optical and near-infrared photometry, spectral classifications, Halpha emission strengths, and rotation periods to examine the interrelationships between coronal and chromospheric activity, rotation, stellar mass, and internal structure for a statistically significant sample of pre-main-sequence stars. A total of 300 distinct X-ray sources can be identified with optical or near-infrared counterparts. The sources are concentrated within three regions of the cluster: in the vicinity of S Mon, within the large emission/reflection nebulosity southwest of S Mon, and along the broad ridge of molecular gas that extends from the Cone Nebula to the NGC 2264 IRS 2 field.
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- ID:
- ivo://CDS.VizieR/J/ApJ/677/401
- Title:
- Xray properties of protostars in ONC
- Short Name:
- J/ApJ/677/401
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin and evolution of the X-ray emission in very young stellar objects (YSOs) are not yet well understood because it is very hard to observe YSOs in the protostellar phase. Using COUP data, we study the X-ray properties of stars in the ONC in different evolutionary classes: luminosities, hydrogen column densities N_H_, effective plasma temperatures, and time variability are compared to understand if the interaction between the circumstellar material and the central object can influence the X-ray emission. We have assembled the deepest and most complete photometric catalog of objects in the ONC region from the UV to 8um using data from the HST Treasury Program; deep and almost simultaneous UBVI and JHK images taken, respectively, with WFI at ESO 2.2m and ISPI at CTIO 4m telescopes; and Spitzer IRAC imaging. We select high-probability candidate Class 0-I protostars, a sample of "bona fide" Class II stars, and a set of Class III stars with IR emission consistent with normal photospheres. Our principal result is that Class 0-Ia objects are significantly less luminous in X-rays, in both the total and hard bands, than the more evolved Class II stars with mass larger than 0.5M_{sun}_; the latter show X-ray luminosities similar to those of Class 0-Ib stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/2485
- Title:
- X-rays from the star-forming complex W40
- Short Name:
- J/ApJ/725/2485
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The young stellar cluster illuminating the W40 HII region, one of the nearest massive star-forming regions, has been observed with the ACIS detector on board the Chandra X-ray Observatory. Due to its high obscuration, this is a poorly studied stellar cluster with only a handful of bright stars visible in the optical band, including three OB stars identified as primary excitation sources. We detect 225 X-ray sources, of which 85% are confidently identified as young stellar members of the region. Two potential distances of the cluster, 260pc and 600pc, are used in the paper.
- ID:
- ivo://CDS.VizieR/J/A+A/490/113
- Title:
- X-ray sources in NGC 752
- Short Name:
- J/A+A/490/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While observational evidence shows that most of the decline in a star's X-ray activity occurs between the age of the Hyades (~8x10^8yr) and that of the Sun, very little is known about the evolution of stellar activity between these ages. To gain information on the typical level of coronal activity at a star's intermediate age, we studied the X-ray emission from stars in the 1.9Gyr old open cluster NGC 752. We analysed a ~140ks Chandraobservation of NGC 752 and a ~50ks XMM-Newtonobservation of the same cluster. We detected 262 X-ray sources in the Chandra data and 145 sources in the XMM-Newton observation. Around 90% of the catalogued cluster members within Chandra's field-of-view are detected in the X-ray. The X-ray luminosity of all observed cluster members (28 stars) and of 11 cluster member candidates was derived.
- ID:
- ivo://CDS.VizieR/J/MNRAS/426/2917
- Title:
- X-rays sources in Trumpler 37
- Short Name:
- J/MNRAS/426/2917
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rich young stellar clusters produce HII regions whose expansion into the nearby molecular cloud is thought to trigger the formation of new stars. However, the importance of this mode of star formation is uncertain. This investigation seeks to quantify triggered star formation (TSF) in IC 1396A (aka the Elephant Trunk Nebula), a bright-rimmed cloud (BRC) on the periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37 cluster. X-ray selection of young stars from Chandra X-ray Observatory data is combined with existing optical and infrared surveys to give a more complete census of the TSF population. Over 250 young stars in and around IC 1396A are identified; this doubles the previously known population. A spatio-temporal gradient of stars from the IC 1396A cloud towards the primary ionizing star HD 206267 is found.
- ID:
- ivo://CDS.VizieR/J/ApJ/525/466
- Title:
- Young low-mass stars and brown dwarfs in IC 348
- Short Name:
- J/ApJ/525/466
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present new results from a continuing program to identify and characterize the low-mass stellar and substellar populations in the young cluster IC 348 (0.5 - 10 Myr). Optical spectroscopy has revealed young objects with spectral types as late as M8.25. The intrinsic J-H and H-K colors of these sources are dwarflike, whereas the R-I and I-J colors appear intermediate between the colors of dwarfs and giants. Furthermore, the spectra from 6500 to 9500 {AA} are reproduced well with averages of standard dwarf and giant spectra, suggesting that such averages should be used in the classification of young late-type sources.
- ID:
- ivo://CDS.VizieR/J/A+A/485/931
- Title:
- Young stars and brown dwarfs in Ori OB1b
- Short Name:
- J/A+A/485/931
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here exhaustive lists of known young stars and new candidate members around Alnilam and Mintaka in the Ori OB1b association as well as of fore- and background sources. A total of 133 stars display features of extreme youth, including early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list additional 74 known objects that might belong to the association. This compilation of tables can serve as an input for characterisation of the stellar and high-mass substellar populations in the Orion Belt.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A29
- Title:
- Young stellar clusters in the Rosette
- Short Name:
- J/A+A/557/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Rosette complex is a well studied region of the galactic plane which presents the apparent characteristics of a triggered star forming region. This is however still debated as no strong evidence corroborates this statement. We focused on characterizing the young stellar population in the Rosette to improve our understanding of the processes that regulate the star formation in this region. We propose an original method relying on the joint analysis of the star color and density in the near-infrared. It yielded the identification of 13 clusters, 2 of them being new discoveries. Based on their spectral index from UKIDSS K-band to WISE W3-band, we identified 535 YSO candidates within these cluster boundaries.
- ID:
- ivo://CDS.VizieR/J/MNRAS/419/1887
- Title:
- Young stellar objects in NGC 6823
- Short Name:
- J/MNRAS/419/1887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6823 is a young open cluster that lies at a distance of ~2kpc in the Vulpecula OB1 association. Previous studies using CCD photometry and spectroscopy have identified a Trapezium system of bright O- and B-type stars at its centre, along with several massive O-, B- and A-type stars in the cluster. We present optical VRI and near-infrared JHK photometric observations, complemented with Spitzer/Infrared Array Camera archival data, with an aim to identify the young low-mass population and the disc candidates in this region. Our survey reaches down to I~22mag and K_s_~18mag. There is significant differential reddening within the cluster. We find a bimodal distribution for A_V_, with a peak at ~3mag and a broader peak at ~10mag. We have classified the sources based on the [4.5]-[8] colour, which is least affected by extinction. We find a ~20 per cent fraction of Class I/Class II young stellar objects (YSOs) in the cluster, while a large 80 per cent fraction of the sources have a Class III classification. We have made use of the INT Photometric H{alpha} Survey (IPHAS) in order to probe the strength in H{alpha} emission for this large population of Class III sources. Nearly all of the Class III objects have photospheric (r'-H{alpha}) colours, implying an absence of H{alpha} in emission. This large population of Class III sources is thus likely the extinct field star population rather than the discless YSOs in the cluster. There is a higher concentration of the Class I/II systems in the eastern region of the cluster and close to the central Trapezium. The western part of the cluster mostly contains Class III/field stars and seems devoid of disc sources. We find evidence of a pre-main-sequence population in NGC 6823, in addition to an upper main-sequence population. The pre-main-sequence population mainly consists of young disc sources with ages between ~1 and 5Myr, and at lower masses of ~0.1-0.4M_{sun}_. There may be a possible mass-dependent age spread in the cluster, with the older stars being more massive than the younger ones. The presence of young disc sources in NGC 6823 indicates similar star formation properties in the outer regions of the Galaxy as observed for young clusters in the solar neighbourhood.
- ID:
- ivo://CDS.VizieR/J/ApJ/575/354
- Title:
- Young stellar objects in the NGC 1333
- Short Name:
- J/ApJ/575/354
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 1333, a highly active star formation region within the Perseus molecular cloud complex, has been observed with the ACIS-I detector on board the Chandra X-Ray Observatory. In our image with a sensitivity limit of ~19^28^erg/s, we detect 127 X-ray sources, most with subarcsecond positional accuracy. While 32 of these sources appear to be foreground stars and extragalactic background, 95 X-ray sources are Identified with known cluster members.