The extended main-sequence turn-off of the Milky Way open cluster Collinder 347

ABSTRACT We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal content. However, the G versus GBP − GRP colour–magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution, and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H] = −0.4 dex), with a present-day mass of 3.3 × 103 M⊙. The cluster exhibits an extended main-sequence turn-off (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation, and metallicity spread yields an eMSTO of ∼340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages.

Dust emission from the atomic and molecular gas in M 33: a changing β

We use the very recently completed high-resolution IRAM CO survey of M33 with the high-resolution HI observations (published by Gratier et al. 2010, A&A, 522, 3) and Herschel Far-IR and submillimeter mapping observations to study how the dust behaves in the molecular and atomic gas phases of the interstellar medium (ISM). M33 is a “young" object in that it is gas-rich with a young stellar population and low metallicity as compared to large spirals like the Milky Way or Andromeda. Nonetheless, it is very clearly a spiral galaxy with a thin and reasonably axisymmetric disk. As such, it can be viewed as a stepping stone towards less evolved objects like magellanic irregulars (including the LMC and SMC) and perhaps distant objects in the early universe. More specifically, we look for radial variations in the dust emission spectrum (β parameter) as well as comparing regions dominated by either H2 or HI. The grey-body emission spectrum flattens (lower β) with galactocentric distance and generally is flatter in the atomic medium as compared to the molecular gas.

Refining the true parameters of the open cluster NGC 4852

NGC 4852 is a moderately compact cluster centered at α2000 = 13 : 00 : 09; δ = −59 : 36 : 48, located near the center of an Hα superring. This cluster forms part of an extended region including young stellar aggregates inside a circle with a radius of 3 degrees, where many show an abundance of emission line stars. In the field of this cluster, two stars of known type exist: Wray 15–1039 (emission-line object) and CD −58:4845 (emission-line star). We do not yet know whether the Be phase is transient or whether it is just what randomly happens in some hot stars. It appears that Be star may be found even in clusters as old as 70 Myr with a high occurrence rate in clusters of 25–27 Myr old. A recent photometric survey in NGC 4852 down to V = 22 – 23 mag established that NGC 4852 is about 200 – 250 Myr old, located at 1.1 kpc from the Sun and with a mean E(B − V) = 0.45 mag. Since the presence of potential Be-type stars in the cluster area suggests it may be a very young object instead of moderately old, we decided to carry out spectroscopy for 33 selected stars and CCD UBVI photometry for the bright objects in the cluster area. This way, we attempt to clarify their evolutionary state and include them in the framework of emission-line stars and open clusters. From our analysis, we agree with the cluster distance and reddening determined by earlier studies, but we derive that the age of NGC 4852 is younger than 40 Myr.

Dust, HII and molecules towards OH and H2O masers

Radio synthesis observations made with the BIMA interferometer at 29, 86 and 216 GHz are presented for twelve galactic fields containing multiple interstellar OH and H2O maser sites. A dusty molecular cloud was found at 20 of the 23 maser sites in the fields studied. The clouds have masses in the range 50 to 800 M⊙ and diameters between 0.1 and 0.5 pc.The data show that most masers are located near the centers of massive, dusty molecular cores. The cores appear to be centrally condensed and internally excited. These results suggest that most masers found in star-forming regions are associated with a massive young object at the center of a collapsing molecular cloud. The kinematics of the core gas, and association with ultra-compact HII regions, implies that the duration of the maser phase includes collapse, expansion and early formation of an HII region.

G305.8 - 0.2: A Young Object with a Dust and Gas Envelope

The H2O maser source in G305.8 - 0.2 was first detected by Haynes et al. (1984). Inspection of the Southern Hemisphere radio surveys did not show any strong compact HII region or water maser placed nearby this source. The IRAS point source catalog (2.0) shows a strong source in the direction of the maser. We analysed the temporal variation and line profile of the H2O maser emission and discussed the nature of its associated IRAS source. These source characteristics seem compatible with the hypothesis that the maser is associated with a protostellar disk around an early-type star of spectral type 07 to 09 surrounded by a spherical shell of gas and dust.

The Atmosphere of a Probably Very Young by Dra-Type Flare Star

ABSTRACTThe flare star Gliese 182 (dM0.5e) seems to be only known single BY Dra type that presents Li in its atmosphere. This characteristic and others, principally activity, and high rotation, indicate that probably this is a very young object. We analyse in this work the possibility to interpret with a single typical model for a dMe atmosphere, some observed lines of Gliese 182 and to predict others. The lines belong to the following atoms; Li I, H I, He I, He II, C I, C II. A relatively good agreement exists only for neutral lines but not for ionized lines. The upper chromosphere and transition region must be studied in more detail. Some comparison are made with the UV observations of the double star BY Dra. Empirical relatively high X-ray fluxes are predicted for both stars. The Li abundance of Gliese 182 is confirmed to be similar to that of the interstellar medium.