Distinguishing post-AGB impostors in a sample of pre-main sequence stars

Vieira, Rodrigo G.; Gregorio-Hetem, J.; Hetem, A.; Stasińska, G.; Szczerba, R.

doi:10.1051/0004-6361/201015592

Cited by 15 publications

(17 citation statements)

References 86 publications

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“…asymptotic giant branch (AGB) stars, classical Be stars, star-forming galaxies, and active galactic nucleus (AGN) which have been frequently misclassified as YSOs in the past (see e.g. Vieira et al 2011). However, given the very young ages and distances that we derived in this study for the Corona-Australis stars, we can discard the existence of such contaminants in our sample.…”

Section: Relative Ages Of the Two Populationsmentioning

confidence: 80%

Corona-Australis DANCe

Galli

Bouy

Olivares

et al. 2020

A&A

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Context. Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet. Aims. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis. Methods. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photometric data set over a field of 128 deg2 around the dark clouds of the region. Results. We identify 313 high-probability candidate members to the Corona-Australis association, 262 of which had never been reported as members before. Our sample of members covers the magnitude range between G ≳ 5 mag and G ≲ 20 mag, and it reveals the existence of two kinematically and spatially distinct subgroups. There is a distributed “off-cloud” population of stars located in the north of the dark clouds that is twice as numerous as the historically known “on-cloud” population that is concentrated around the densest cores. By comparing the location of the stars in the HR-diagram with evolutionary models, we show that these two populations are younger than 10 Myr. Based on their infrared excess emission, we identify 28 Class II and 215 Class III stars among the sources with available infrared photometry, and we conclude that the frequency of Class II stars (i.e. “disc-bearing” stars) in the on-cloud region is twice as large as compared to the off-cloud population. The distance derived for the Corona-Australis region based on this updated census is d = 149.4 +0.4−0.4 pc, which exceeds previous estimates by about 20 pc. Conclusions. In this paper we provide the most complete census of stars in Corona-Australis available to date that can be confirmed with Gaia data. Furthermore, we report on the discovery of an extended and more evolved population of young stars beyond the region of the dark clouds, which was extensively surveyed in the past.

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Section: Relative Ages Of the Two Populationsmentioning

confidence: 80%

Corona-Australis DANCe

Galli

Bouy

Olivares

et al. 2020

A&A

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“…The infrared SEDs of evolved stars can be quite similar to those of YSOs, and thus the nature of objects selected by criteria based on infrared excess alone is not immediately clear and can lead to ambiguities (e.g. Vieira et al 2011). …”

Section: Evolved Starsmentioning

confidence: 99%

Herschelfar-infrared observations of the Carina Nebula complex

Gaczkowski

Preibisch

Ratzka

et al. 2012

A&A

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Context. The Carina Nebula represents one of the largest and most active star forming regions known in our Galaxy. It contains numerous very massive (M > ∼ 40 M ) stars that strongly affect the surrounding clouds by their ionizing radiation and stellar winds. Aims. Our recently obtained Herschel PACS and SPIRE far-infrared maps cover the full area (≈8.7 deg 2 ) of the Carina Nebula complex (CNC) and reveal the population of deeply embedded young stellar objects (YSOs), most of which are not yet visible in the mid-or near-infrared. Methods. We study the properties of the 642 objects that are independently detected as point-like sources in at least two of the five Herschel bands. For those objects that can be identified with apparently single Spitzer counterparts, we use radiative transfer models to derive information about the basic stellar and circumstellar parameters. Results. We find that about 75% of the Herschel-detected YSOs are Class 0 protostars. The luminosities of the Herschel-detected YSOs with SED fits are restricted to values of ≤5400 L , their masses (estimated from the radiative transfer modeling) range from ≈1 M to ≈10 M . Taking the observational limits into account and extrapolating the observed number of Herschel-detected protostars over the stellar initial mass function suggest that the star formation rate of the CNC is ∼0.017 M /year. The spatial distribution of the Herschel YSO candidates is highly inhomogeneous and does not follow the distribution of cloud mass. Rather, most Herschel YSO candidates are found at the irradiated edges of clouds and pillars. The far-infrared fluxes of the famous object η Car are about a factor of two lower than expected from observations with the Infrared Space Observatory obtained 15 years ago; this difference may be a consequence of dynamical changes in the circumstellar dust in the Homunculus Nebula around η Car. Conclusions. The currently ongoing star formation process forms only low-mass and intermediate-mass stars, but no massive (M > ∼ 20 M ) stars. The characteristic spatial configuration of the YSOs provides support to the picture that the formation of this latest stellar generation is triggered by the advancing ionization fronts.

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“…We note that the number of YSOs in the 15 km s −1 cloud is too small and statistically unimportant, therefore the derived total stellar mass may have a large uncertainty. The total stellar mass of the 50 km s −1 cloud probably is significantly overestimated since the lower limit mass (2.7 M ) in the IMF derived from the K s band magnitude is too high and its total YSO number may be contaminated by foreground YSOs or circumstellar material such as post-AGB stars at such a far distance (5.40 kpc) (Vieira et al 2011). The discussions below therefore only focus on the 27 km s −1 cloud.…”

Section: Star Formation Efficiencies and Ratesmentioning

confidence: 99%

Molecular clouds and star formation toward the Galactic plane within 216.25° ≤l≤ 218.75° and −0.75° ≤b≤ 1.25°

Gong

Mao

Fang

et al. 2016

A&A

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Context. Molecular clouds trace the spiral arms of the Milky Way and all its star forming regions. Large-scale mapping of molecular clouds will provide an approach to understand the processes that govern star formation and molecular cloud evolution. Aims. As a part of the Milky Way Imaging Scroll Painting (MWISP) survey, the aim is to study the physical properties of molecular clouds and their associated star formation toward the Galactic plane within 216.25• ≤ l ≤ 218.75• and −0.75• , which covers the molecular cloud complex S287. Methods. Using the 3 × 3 Superconducting Spectroscopic Array Receiver (SSAR) at the PMO-13.7m telescope, we performed a simultaneous 12 CO (1-0), 13 CO (1-0), C 18 O (1-0) mapping toward molecular clouds in a region encompassing 3.75 square degrees. We also make use of archival data to study star formation within the molecular clouds. Results. We reveal three molecular clouds, the 15 km s −1 cloud, the 27 km s −1 cloud, and the 50 km s −1 cloud, in the surveyed region. The 50 km s −1 cloud is resolved with an angular resolution of ∼1 for the first time. Investigating their morphology and velocity structures, we find that the 27 km s −1 cloud is likely affected by feedback from the stellar association Mon OB3 and the 50 km scloud is characterized by three large expanding molecular shells. The surveyed region is mapped in C 18 O (1-0) for the first time. We discover seven C 18 O clumps that are likely to form massive stars, and 15 dust clumps based on the Bolocam Galactic Plane Survey (BGPS) archive data. Using infrared color-color diagrams, we find 56 Class I and 107 Class II young stellar object (YSO) candidates toward a slightly larger region of 5.0 square degrees. Based on the distribution of YSO candidates, an overdensity is found around the HII region S287 and the intersection of two shells; this is probably indicative of triggering. The star formation efficiency (SFE) and rate (SFR) of the 27 km s −1 cloud are discussed. Comparing the observed values of the filament S287-main with fragmentation models, we suggest that turbulence controls the large-scale fragmentation in the filament, while gravitational fragmentation plays an important role in the formation of YSOs on small scales. We find that star-forming gas tends to have a higher excitation temperature, a higher 13 CO (1-0) opacity, and a higher column density than non-star-forming gas, which is consistent with the point that star formation occurs in denser gas and star-forming gas is heated by YSOs. Using the 1.1 mm dust emission to trace dense gas, we obtain a dense gas fraction of 2.7-10.4% for the 27 km s −1 cloud.Key words. surveys -ISM: clouds -stars: formation -radio lines: ISM -ISM: kinematics and dynamics IntroductionMolecular clouds are also known as stellar nurseries because they are the densest parts of the interstellar medium that may gravitationally collapse, and thus create protostars (e.g., Shu et al. 1987;Kennicutt & Evans 2012). Molecular clouds comprise a significant fraction of the total mass of in...

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Distinguishing post-AGB impostors in a sample of pre-main sequence stars

Cited by 15 publications

References 86 publications

Corona-Australis DANCe

Corona-Australis DANCe

Herschelfar-infrared observations of the Carina Nebula complex

Molecular clouds and star formation toward the Galactic plane within 216.25° ≤l≤ 218.75° and −0.75° ≤b≤ 1.25°

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