- 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.
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Search Results
- 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/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/AJ/152/75
- Title:
- Photometric survey of IC 2391, {eta} Cha, and USco
- Short Name:
- J/AJ/152/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The past two decades have seen a significant advancement in the detection, classification, and understanding of exoplanets and binaries. This is due, in large part, to the increase in use of small-aperture telescopes (<20cm) to survey large areas of the sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied to date consists of main-sequence or evolved objects, leading to a dearth of knowledge of properties at early times (<50Myr). Only a dozen binaries and one candidate transiting Hot Jupiter are known among pre-main-sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well characterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects, which can mask and mimic eclipse signals. Hence, a dramatic increase in the number of young systems with high-quality observations is highly desirable to guide further theoretical developments. We have recently completed a photometric survey of three nearby (<150pc) and young (<50Myr) moving groups with a small-aperture telescope. While our survey reached the requisite photometric precision, the temporal coverage was insufficient to detect Hot Jupiters. Nevertheless, we discovered 346 pre-main-sequence binary candidates, including 74 high-priority objects for further study.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A41
- Title:
- Photometric variability of massive YSOs
- Short Name:
- J/A+A/619/A41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Vista Variables in the Via Lactea (VVV) survey has allowed for an unprecedented number of multi-epoch observations of the southern Galactic plane. In a recent paper, 13 massive young stellar objects (MYSOs) have already been identified within the highly variable ({Delta}Ks>1mag) YSO sample of another published work. This study aims to understand the general nature of variability in MYSOs. Here we present the first systematic study of variability in a large sample of candidate MYSOs. We examined the data for variability of the putative driving sources of all known Spitzer extended green objects (EGOs; 270) and bright 24um sources coinciding with the peak of 870um detected ATLASGAL clumps (448), a total of 718 targets. Of these, 190 point sources (139 EGOs and 51 non-EGOs) displayed variability (IQR>0.05, {Delta}Ks>0.15mag). 111 and 79 light-curves were classified as periodic and aperiodic respectively. Light-curves have been sub-classified into eruptive, dipper, fader, short-term-variable and long-period-variable-YSO categories. Lomb-Scargle periodogram analysis of periodic light-curves was carried out. 1-870um spectral energy distributions of all the variable sources were fitted with YSO models to obtain the representative properties of the variable sources. 41% of the variable sources are represented by >4M_{sun}_ objects, and only 6% were modelled as >8M_{sun}_ objects. The highest-mass objects are mostly non-EGOs, and deeply embedded, as indicated by nearly twice the extinction when compared with EGO sources. By placing them on the HR diagram we show that most of the lower mass, EGO type objects are concentrated on the putative birth-line position, while the luminous non-EGO type objects group around the zero-age-main-sequence track. Some of the most luminous far infrared (FIR) sources in the massive clumps and infrared quiet driving sources of EGOs have been missed out by this study owing to an uniform sample selection method. A high rate of detectable variability in EGO targets (139 out of 153 searched) implies that near-infrared variability in MYSOs is closely linked to the accretion phenomenon and outflow activity.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/896
- Title:
- Photometry in the cometary globule Ori I-2
- Short Name:
- J/ApJ/706/896
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the young stellar population in and near the cometary globule Ori I-2. The analysis is based on deep Nordic Optical Telescope R-band and H{alpha} images, JCMT SCUBA 450 and 850um images combined with near-infrared Two Micron All Sky Survey (2MASS) photometry and mid-infrared archival Spitzer images obtained with the Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, and 8um), and MIPS (24 and 70um) instruments. We identify a total of 125 sources within the 5'x5' region imaged by the IRAC. Of these sources, 87 are detected in the R-band image and 51 are detected in the 2MASS. Ori I-2 shows clear evidence of triggered star formation with four young low-luminosity pre-main-sequence (PMS) stars embedded in the globule. At least two, possibly as many as four, additional low-mass PMS objects were discovered in the field which are probably part of the young {sigma} Orionis cluster. Among the PMS stars which have formed in the globule, MIR-54 is a young, deeply embedded Class 0/I object; MIR-51 and 52 are young Class II sources, while MIR-89 is a more evolved, heavily extincted Class II object with its apparent colors mimicking a Class 0/I object. The Class 0/I object MIR-54 coincides with a previously known IRAS source and is a strong submillimeter source. It is most likely the source for the molecular outflow and the large parsec-scale Herbig-Haro (HH) flow. However, the nearby Class II source, MIR-52, which is strong a H{alpha} emission line star, also appears to drive an outflow approximately aligned with the outflow from MIR-54, and because of the proximity of the two outflows, either star could contribute. MIR-89 appears to excite a low-excitation HH object, HH 992, discovered for the first time in this study.
- ID:
- ivo://CDS.VizieR/J/A+A/483/209
- Title:
- Photometry of a stellar cluster near IRAS 07141-092
- Short Name:
- J/A+A/483/209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution optical UBVRI and H{alpha} images obtained with ALFOSC mounted on the Nordic Optical Telescope (NOT), near-infrared JHK_S_ images obtained with NOTCam at the Nordic Optical Telescope, and VLT/ISAAC images obtained through the H_2_ (2.12{mu}m) filter were all used to make photometric and morphological studies of the point sources and the nebula seen towards Sh2-294. Identification of PMS members was done using three different methods: comparison with isochrones in optical colour-magnitude diagrams and detection of either near-IR excess or H{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A99
- Title:
- Photometry of EXors from Asiago plates
- Short Name:
- J/A+A/602/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- EXor objects are young variables that show episodic variations of brightness commonly associated to enhanced accretion outbursts. With the aim of investigating the long-term photometric behaviour of a few EXor sources, we present here data from the archival plates of the Asiago Observatory, showing the Orion field where the three EXors V1118, V1143, and NY are located. A total of 484 plates were investigated, providing a total of more than 1000 magnitudes for the three stars, which cover a period of about 35yrs between 1959 to 1993. We then compared our data with literature data. Apart from a newly discovered flare-up of V1118, we identify the same outbursts already known, but we provide two added values: (i) a long-term sampling of the quiescence phase; and (ii) repeated multi-colour observations (BVRI bands). The former allows us to give a reliable characterisation of the quiescence, which represents a unique reference for studies that will analyze future outbursts and the physical changes induced by these events. The latter is useful for confirming whether the intermittent increases of brightness are accretion-driven (as in the case of V1118), or extinction-driven (as in the case of V1143). Accordingly, doubts arise about the V1143 classification as a pure EXor object. Finally, although our plates do not separate NY Ori and the star very close to it, they indicate that this EXor did not undergo any major outbursts during our 40yrs of monitoring.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A95
- Title:
- Photometry of the young open cluster Pismis 24
- Short Name:
- J/A+A/573/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study of the stellar population of the young open cluster Pismis 24 (RA~17:24:44, DE~-34:12). Observations were carried out through JHKs filters with SofI at NTT (ESO). Photometry in the IRAC (onboard satellite Spitzer) bands (3.6, 4.5, 5.8, and 8.0-micron) was performed on deep archive images. Optical photometry in the Cousins VI bands was performed on WFC2 (onboard the HST) archive images. High-resolution X-ray photometry with ACIS (onboard satellite Chandra) was taken from Wang et al. (2007). Source coordinates were obtained by matching SofI Ks sources to 2MASS K sources. Table 1 lists the sources retrieved in the SofI field (without VI photometry). Table 2 contains the subsample of sources from Table 1 falling in the smaller WFC2 field (including VI photometry).
- ID:
- ivo://CDS.VizieR/J/ApJ/786/97
- Title:
- Photospheric properties of T Tauri stars
- Short Name:
- J/ApJ/786/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.
