- ID:
- ivo://CDS.VizieR/J/A+A/508/1313
- Title:
- Orion pre-main sequence RIJH light curves
- Short Name:
- J/A+A/508/1313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed an intensive photometric monitoring of the PMS stars falling in a field of about 10x10 arcminutes in the vicinity of the Orion Nebula Cluster (ONC). Photometric data were collected between November 2006 and January 2007 with the REM telescope in the VRIJHK' bands. The largest number of observations is in the I band (about 2700 images) and in J and H bands (about 500 images in each filter). From the observed rotational modulation, induced by the presence of surface inhomogeneities, we derived the rotation periods for 16 stars and improved previous determinations for the other 13. The analysis of the spectral energy distributions and, for some stars, of high-resolution spectra provided us with the main stellar parameters (luminosity, effective temperature, mass, age, and vsini). We also report the serendipitous detection of two strong flares in two of these objects. In most cases, the light-curve amplitudes decrease progressively from the R to H band as expected for cool starspots, while in a few cases, they can only be modelled by the presence of hot spots, presumably ascribable to magnetospheric accretion. The application of our own spot model to the simultaneous light curves in different bands allowed us to deduce the spot parameters and particularly to disentangle the spot temperature and size effects on the observed light curves.
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- ID:
- ivo://CDS.VizieR/J/ApJS/78/239
- Title:
- Orion stars CO-added IRAS fluxes catalog
- Short Name:
- J/ApJS/78/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog of co-added IRAS fluxes for the pre-main-sequence objects in the Herbig-Bell catalog (HBC) is presented. This catalog doubles the number of HBC stars with detected IRAS fluxes and provides improved flux values for the previously known sources. Noise levels are given for all HBC fields in each band, permitting upper limits to be estimated for all undetected sources.
- 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/625/A13
- Title:
- Outburst of V1318 Cyg S (LkHa 225)
- Short Name:
- J/A+A/625/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young double star V1318 Cyg, which is associated with a small isolated star-forming region around HAeBe star BD+40 4124, has very unusual photometric and spectral behavior. We present results of photometric and spectroscopic observations in the optical range. We carried out BVRI CCD photometric observations of V1318 Cyg from 2015 Sept. to 2017 July. For the same period we acquired medium- and low-resolution spectra. Observations were performed with the 2.6 m telescope of the Byurakan observatory. We also analyzed the images of this field in IPHAS and other surveys. We analyze the historical light curve for V1318 Cyg and demonstrate that the southern component, V1318 Cyg S, after being rather bright in the 1970s (V~14 mag) started to lower its brightness and in 1990 became practically invisible in the optical. After its reappearance in the second half of the 1990s the star started to become very slowly brighter. Between 2006 and 2010 V1318 Cyg S started brightening more quickly, and in 2015 had become brighter by more than five magnitudes in visible light. Since this time V1318 Cyg S has remained at this maximum. Its spectrum shows little variability and consists of a mixture of emission and absorption lines, which has allowed for estimates of its spectral type as early Ae, with obvious evidence of matter outflow. We derive its current A(V)~7.2 and L=750L_(sun)_ thus confirming that V1318 Cyg S should belong to the Herbig Ae stars, making it, along with BD+40 4124 and V1686 Cyg, the third luminous young star in the group. It is very probable that we observe V1318 Cyg S near the pole and that the inclination of its dense and slow (<100km/s) outflow is low. The unusual variability and other features of V1318 Cyg S make it difficult to classify this star among known types of eruptive young stars. It could be an extreme, higher-mass example of an EXor, or an object of intermediate class between EXors and FUors, like V1647 Ori.
- ID:
- ivo://CDS.VizieR/J/AJ/152/198
- Title:
- Periods of 4-10 Myr old T Tauri members of Orion OB1
- Short Name:
- J/AJ/152/198
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most existing studies of the angular momentum evolution of young stellar populations have focused on the youngest (<~1-3Myr) T Tauri stars. In contrast, the angular momentum distributions of older T Tauri stars (~4-10Myr) have been less studied, even though they hold key insights to understanding stellar angular momentum evolution at a time when protoplanetary disks have largely dissipated and when models therefore predict changes in the rotational evolution that can in principle be tested. We present a study of photometric variability among 1974 confirmed T Tauri members of various subregions of the Orion OB1 association, and with ages spanning 4-10Myr, using optical time series from three different surveys. For 564 of the stars (~32% of the weak-lined T Tauri stars and ~13% of the classical T Tauri stars in our sample) we detect statistically significant periodic variations, which we attribute to the stellar rotation periods, making this one of the largest samples of T Tauri star rotation periods yet published. We observe a clear change in the overall rotation period distributions over the age range 4-10Myr, with the progressively older subpopulations exhibiting systematically faster rotation. This result is consistent with angular momentum evolution model predictions of an important qualitative change in the stellar rotation periods starting at ~5Myr, an age range for which very few observational constraints were previously available.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/116
- Title:
- Photmetry and spectroscopy of PMS stars in NGC 2264
- Short Name:
- J/ApJ/831/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The timescale of cluster formation is an essential parameter in order to understand the formation process of star clusters. Pre-main sequence (PMS) stars in nearby young open clusters reveal a large spread in brightness. If the spread were considered to be a result of a real spread in age, the corresponding cluster formation timescale would be about 5-20Myr. Hence it could be interpreted that star formation in an open cluster is prolonged for up to a few tens of Myr. However, difficulties in reddening correction, observational errors, and systematic uncertainties introduced by imperfect evolutionary models for PMS stars can result in an artificial age spread. Alternatively, we can utilize Li abundance as a relative age indicator of PMS star to determine the cluster formation timescale. The optical spectra of 134 PMS stars in NGC 2264 have been obtained with MMT/Hectochelle. The equivalent widths have been measured for 86 PMS stars with a detectable Li line (3500<{T}_eff[K]_<=6500).
- ID:
- ivo://CDS.VizieR/J/ApJ/728/69
- Title:
- Photoelectric photometry of V410 Tauri
- Short Name:
- J/ApJ/728/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Doppler images of the weak-lined T Tauri star V410 Tau obtained with two different Doppler-imaging codes. The images are consistent and show a cool extended spot, symmetric about the pole, at a temperature approximately 750K below the average photospheric value. Smaller cool spots are found fairly uniformly distributed at latitudes below the polar cap with temperatures about 450K below the average photospheric temperature. Resolution on the stellar surface is limited to about 7{deg} of arc, so structure within these spots is not visible. Also at lower latitudes are hotter features with temperatures up to 1000K above the photosphere. A trial Doppler image using a TiO molecular feature reproduced the cool polar cap at a temperature about 100K below the value from the atomic line images. The equatorial features, however, were not properly reproduced since Doppler imaging relies on information in the wings of lines for reconstructing equatorial features, and for V410 Tau these molecular band lines overlap. In 1993, V410 Tau had a large photometric amplitude resulting from the concentration of cool spots on the hemisphere of the star visible at phase 0{deg}, a phenomenon known as preferred longitude. In contrast, the small photometric amplitude observed currently is due to a strong symmetric polar spot and the uniform distribution in longitude of equatorial cool and warm spots. This redistribution of surface features may be the beginning of a slow "flip-flop" for V410 Tau where spot locations alternate between preferred longitudes. Flare events linked to two of the hotter spots in the Doppler image were observed.
- 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/A+AS/113/473
- Title:
- Photometric observations of PMS objects
- Short Name:
- J/A+AS/113/473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the observational data of a photometric monitoring of 24 pre-main sequence objects: T Tauri stars, Ae/Be Herbig stars and some unclassified objects. Observations were carried out from July 1988 to August 1992, using the UBV(RI)_c system. Variability with time scales from days to years and amplitudes in the V band larger than 0.1 mag is found for a part of this sample. The analysis of the possible causes of this variability are discussed in separate papers (Fernandez & Eiroa 1995a,b).
