- ID:
- ivo://CDS.VizieR/J/other/PASA/32.21
- Title:
- Long-Term Multicolour Photometry of YSOs
- Short Name:
- J/other/PASA/32.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results from long-term multicolour optical photometric observations of the pre-main sequence stars FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cyg collected during the period from 1997 June to 2014 December are presented. The objects are located in the dense molecular cloud L935, named 'Gulf of Mexico', in the field between the North America and Pelican nebulae. All stars from our study exhibit strong photometric variability in all optical passbands. Using our BVRI observations and data published by other authors, we tried to define the reasons for the observed brightness variations. The presented paper is a part of our long-term photometric study of the young stellar objects in the region of 'Gulf of Mexico'.
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- ID:
- ivo://CDS.VizieR/J/ApJS/179/249
- Title:
- Low-luminosity embedded protostar population
- Short Name:
- J/ApJS/179/249
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for all embedded protostars with internal luminosities <=1.0L_{sun}_ in the full sample of nearby, low-mass star-forming regions surveyed by the Spitzer Space Telescope Legacy Project "From Molecular Cores to Planet Forming Disks" (c2d). We present a set of selection criteria used to identify candidates from the Spitzer data and examine complementary data to decide whether each candidate is truly an embedded protostar. Between 75% and 85% of cores classified as starless prior to being observed by Spitzer remain starless to our luminosity sensitivity; the remaining 15%-25% harbor low-luminosity, embedded protostars. We compile complete spectral energy distributions for all 50 objects and calculate standard evolutionary signatures (L_bol_, T_bol_, and L_bol_/L_smm_) and argue that these objects are inconsistent with the simplest picture of star formation, wherein mass accretes from the core onto the protostar at a constant rate.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/654
- Title:
- Low-mass members of Chamaeleon I
- Short Name:
- J/ApJ/684/654
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used images obtained with the Infrared Array Camera and the Multiband Imaging Photometer on board the Spitzer Space Telescope to search for low-mass stars and brown dwarfs with circumstellar disks in the Chamaeleon I star-forming region. Through optical spectroscopy of sources with red colors in these data, we have identified seven new disk-bearing members of the cluster. Three of these objects are probably brown dwarfs, according to their spectral types (M8, M8.5, M8-L0). Three of the other new members may have edge-on disks, based on the shapes of their infrared spectral energy distributions. One of the possible edge-on systems has a steeply rising slope from 4.5 to 24um, indicating that it could be a Class I source (star+disk+envelope) rather than a Class II source (star+disk). If so, then it would be one of the least massive known Class I protostars (M5.75, M~0.1M_{sun}_).
- ID:
- ivo://CDS.VizieR/J/ApJ/752/59
- Title:
- Low-mass population in L1641
- Short Name:
- J/ApJ/752/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an optical photometric and spectroscopic survey of the young stellar population in L1641, the low-density star-forming region of the Orion A cloud south of the Orion Nebula Cluster (ONC). Our goal is to determine whether L1641 has a large enough low-mass population to make the known lack of high-mass stars a statistically significant demonstration of environmental dependence of the upper mass stellar initial mass function (IMF). Our spectroscopic sample consists of IR-excess objects selected from the Spitzer/IRAC survey and non-excess objects selected from optical photometry. We have spectral confirmation of 864 members, with another 98 probable members; of the confirmed members, 406 have infrared excesses and 458 do not. Assuming the same ratio of stars with and without IR excesses in the highly extincted regions, L1641 may contain as many as ~1600 stars down to ~0.1M_{sun}_, comparable within a factor of two to the ONC. Compared to the standard models of the IMF, L1641 is deficient in O and early B stars to a 3{sigma}-4{sigma} significance level, assuming that we know of all the massive stars in L1641.
- ID:
- ivo://CDS.VizieR/J/A+A/515/A75
- Title:
- Low-mass population in {rho} Oph cloud
- Short Name:
- J/A+A/515/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation theories are currently divergent regarding the fundamental physical processes that dominate the substellar regime. Observations of nearby young open clusters allow the brown dwarf (BD) population to be characterised down to the planetary mass regime, which ultimately must be accommodated by a successful theory. We used near-IR deep images (reaching completeness limits of approximately 20.5mag in J, and 18.9mag in H and Ks taken with the Wide Field IR Camera (WIRCam) at the Canada France Hawaii Telescope (CFHT) to identify candidate members of {rho} Oph in the substellar regime. A spectroscopic follow-up of a small sample of the candidates allows us to assess their spectral type, and subsequently their temperature and membership. We select 110 candidate members of the {rho} Ophiuchi molecular cloud, from which 80 have not previously been associated with the cloud. We observed a small sample of these and spectroscopically confirm six new brown dwarfs with spectral types ranging from M6.5 to M8.25.
- ID:
- ivo://CDS.VizieR/J/AJ/145/94
- Title:
- Luminosities of protostars from two Spitzer surveys
- Short Name:
- J/AJ/145/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Motivated by the long-standing "luminosity problem" in low-mass star formation whereby protostars are underluminous compared to theoretical expectations, we identify 230 protostars in 18 molecular clouds observed by two Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We compile complete spectral energy distributions, calculate L_bol_ for each source, and study the protostellar luminosity distribution. This distribution extends over three orders of magnitude, from 0.01L_{sun}_ to 69L_{sun}_, and has a mean and median of 4.3L_{sun}_ and 1.3L_{sun}_, respectively. The distributions are very similar for Class 0 and Class I sources except for an excess of low luminosity (L_bol_<~0.5L_{sun}_) Class I sources compared to Class 0. 100 out of the 230 protostars (43%) lack any available data in the far-infrared and submillimeter (70{mu}m<{lambda}<850{mu}m) and have L_bol_ underestimated by factors of 2.5 on average, and up to factors of 8-10 in extreme cases. Correcting these underestimates for each source individually once additional data becomes available will likely increase both the mean and median of the sample by 35%-40%. We discuss and compare our results to several recent theoretical studies of protostellar luminosities and show that our new results do not invalidate the conclusions of any of these studies. As these studies demonstrate that there is more than one plausible accretion scenario that can match observations, future attention is clearly needed. The better statistics provided by our increased data set should aid such future work.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A20
- Title:
- Lupus YSOs X-shooter spectroscopy
- Short Name:
- J/A+A/600/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass accretion rate, M_acc_, is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (M_{star}_<=2.0M_{sun}_) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III and IV clouds, based on spectroscopic data acquired with the VLT/X-shooter spectrograph. Our study combines the dataset from our previous work with new observations of 55 additional objects. We have investigated 92 YSO candidates in total, 11 of which have been definitely identified with giant stars unrelated to Lupus. The stellar and accretion properties of the 81 bona fide YSOs, which represent more than 90% of the whole class II and transition disc YSO population in the aforementioned Lupus clouds, have been homogeneously and self-consistently derived, allowing for an unbiased study of accretion and its relationship with stellar parameters. The accretion luminosity, L_acc_, increases with the stellar luminosity, L*, with an overall slope of ~1.6, similar but with a smaller scatter than in previous studies. There is a significant lack of strong accretors below L*~=0.1L_{sun}_, where L_acc_ is always lower than 0.01L*. We argue that the L_acc_-L* slope is not due to observational biases, but is a true property of the Lupus YSOs. The log M_acc_-logM* correlation shows a statistically significant evidence of a break, with a steeper relation for M*<=0.2M_{sun}_ and a flatter slope for higher masses. The bimodality of the M_acc_-M* relation is confirmed with four different evolutionary models used to derive the stellar mass. The bimodal behaviour of the observed relationship supports the importance of modelling self-gravity in the early evolution of the more massive discs, but other processes, such as photo-evaporation and planet formation during the YSO's lifetime, may also lead to disc dispersal on different timescales depending on the stellar mass. The sample studied here more than doubles the number of YSOs with homogeneously and simultaneously determined L_acc_ and luminosity, L_line_, of many permitted emission lines. Hence, we also refined the empirical relationships between L_acc_ and L_line_ on a more solid statistical basis.
- ID:
- ivo://CDS.VizieR/J/AJ/150/95
- Title:
- Masses and ages of YSOs in Per OB2
- Short Name:
- J/AJ/150/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a Wide-Field Infrared Survey Explorer based study to identify and characterize young stellar objects (YSOs) in the 12{deg}x12{deg} Perseus OB2 association. A spectral energy distribution (SED) slope in the range of 3.4-12{mu}m and 5{sigma} selection criteria were used to select our initial sample. Further manual inspection reduced our final catalog to 156 known and 119 YSO candidates. The spatial distribution of newly found YSOs all over the field shows an older generation of star formation in which most of its massive members have evolved into main-sequence stars. In contrast, the majority of younger members lie within the Perseus molecular cloud and currently active star-forming clusters such as NGC 1333 and IC 348. We also identified an additional 66 point sources that passed YSO selection criteria but are likely AGB stars. However, their spatial distribution suggests that they may contain a fraction of the YSOs. Comparing our results with the commonly used color-color selections, we found that while the color selection method fails in picking up bright but evolved weak disks, our SED fitting method can identify such sources, including transitional disks. In addition, we have less contamination with background sources such as galaxies, but at a price of losing fainter (J_mag_>12) YSOs. Finally, we employed a Bayesian Monte Carlo SED fitting method to determine the characteristics of each YSO candidate. Distribution of SED slopes and model-driven age and mass confirms separated YSO populations with three suggested age groups of younger than 1Myr old, 1-5Myr old, and older than 5Myr, which agrees with the age of the Per OB2 association and currently star-forming sites within the cloud.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/645
- Title:
- Massive molecular outflows distance-limited sample
- Short Name:
- J/MNRAS/453/645
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed 99 mid-infrared-bright, massive young stellar objects and compact HII regions drawn from the Red MSX source survey in the J=3-2 transition of ^12^CO and ^13^CO, using the James Clerk Maxwell Telescope. 89 targets are within 6kpc of the Sun, covering a representative range of luminosities and core masses. These constitute a relatively unbiased sample of bipolar molecular outflows associated with massive star formation. Of these, 59, 17 and 13 sources (66, 19 and 15 percent) are found to have outflows, show some evidence of outflow, and have no evidence of outflow, respectively. The time-dependent parameters of the high-velocity molecular flows are calculated using a spatially variable dynamic time-scale. The canonical correlations between the outflow parameters and source luminosity are recovered and shown to scale with those of low-mass sources. For coeval star formation, we find the scaling is consistent with all the protostars in an embedded cluster providing the outflow force, with massive stars up to ~30M_{sun}_ generating outflows. Taken at face value, the results support the model of a scaled-up version of the accretion-related outflow-generation mechanism associated with discs and jets in low-mass objects with time-averaged accretion rates of ~ 10^-3^M_{sun}_/yr on to the cores. However, we also suggest an alternative model, in which the molecular outflow dynamics are dominated by the entrained mass and are unrelated to the details of the acceleration mechanism. We find no evidence that outflows contribute significantly to the turbulent kinetic energy of the surrounding dense cores.
- ID:
- ivo://CDS.VizieR/J/A+A/432/921
- Title:
- Massive protostellar candidates
- Short Name:
- J/A+A/432/921
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed two rotational transitions of both CS and C^17^O, and the 1.2mm continuum emission towards a sample of 130 high-mass protostellar candidates with DE<-30{deg}. This work represents the first step of the extension to the southern hemisphere of a project started more than a decade ago aimed at the identification of massive protostellar candidates. Following the same approach adopted for sources with DE>=-30{deg}, we have selected from the IRAS Point Source Catalogue 429 sources which potentially are compact molecular clouds on the basis of their IR colours. The sample has then been divided into two groups according to the colour indices [25-12] and [60-12]: the 298 sources with [25-12]>=0.57 and [60-12]>=1.30 have been called High sources, the remaining 131 have been called Low sources. In this paper, we check the association with dense gas and dust in 130 Low sources. We have obtained a detection rate of ~85% in CS, demonstrating a tight association of the sources with dense molecular clumps.
