Jing-Hua Yuan

Orbital period changes of the nova-like cataclysmic variable AC Cancri: evidence of magnetic braking and an unseen companion

Aims. The source AC Cnc is a nova-like cataclysmic variable containing a white-dwarf primary with a mass of 0.76 M-circle dot and a K2-type secondary with a mass of 0.77 M-circle dot. We intend to study its period changes and search for evidence of magnetic braking and unseen third body. Methods. The period changes were investigated based on the analysis of the O-C curve, which is formed by one new eclipse time together with the others compiled from the literature. Results. A cyclic change with a period of 16.2 yr was found to be superimposed on a long-term period decrease at a rate of. P = -1.24(+/- 0.44) x 10(-8) days/year. Conclusions. It is shown that the mechanism of magnetic activity-driven changes in the quadrupole momentum of the secondary star (Applegates mechanism) does not explain it easily. This period oscillation was plausibly interpreted by a light-travel time effect caused by the presence of a cool M-type dwarf companion (M-3 > 0.097 M-circle dot) in a long orbit (16.2 yr) around the binary. Since the masses of both components are nearly the same, the mass transfer from the lobe-filling secondary to the primary is not efficient to cause the continuous period decrease. It may be strong evidence of an enhanced magnetic stellar wind from the K2-type component. If the Alfen radius of the cool secondary is the same as that of the Sun (i.e., R-A = 15 R-circle dot), the mass-loss rate should be. M-2 = -1.65 x 10(-10) M-circle dot/year. By using the enhanced mass loss proposed by Tout & Eggleton (1988), the mass-loss rate should be. M-2 = -1.18 x 10(-9) M-circle dot/year. In this case, the Alfen radius is determined to be R-A = 5.2 R-circle dot. However, the long-term decrease of the period may be only a part of a long-period (> 100 yr) oscillation caused by the presence of an additional body. To check the conclusions, new precise times of light minimum will be required.

EXPANDING SHELL AND STAR FORMATION IN THE INFRARED DUST BUBBLE N6

We have carried out a multi-wavelength study of the infrared dust bubble N6 to extensively investigate the molecular environs and star-forming activities therein. Mapping observations in 12CO J=1-0 and 13CO J=1-0 performed with the Purple Mountain Observatory 13.7-m telescope have revealed four velocity components. Comparison between distributions of each component and the infrared emission suggests that three components are correlated with N6. There are ten molecular clumps detected. Among them, five have reliable detection in both 12CO and 13CO and have similar LTE and non-LTE masses ranging from 200 to higher than 5,000 M_sun. With larger gas masses than virial masses, these five clumps are gravitationally unstable and have potential to collapse to form new stars. The other five clumps are only reliably detected in 12CO and have relatively small masses. Five clumps are located on the border of the ring structure and four of them are elongated along the shell. This is well in agreement with the collect and collapse scenario. The detected velocity gradient reveals that the ring structure is still under expansion due to stellar winds from the exciting star(s). Furthermore, 99 young stellar objects have been identified based on their infrared colors. A group of YSOs reside inside the ring, indicating active star formation in N6. Although no confirmative features of triggered star formation detected, the bubble and the enclosed HII region have profoundly reconstructed the natal could and altered the dynamics therein.

Planck Cold Clumps in the λ Orionis Complex. I : Discovery of an Extremely Young Class 0 Protostellar Object and a Proto-brown Dwarf Candidate in the Bright-rimmed Clump PGCC G192.32-11.88

We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the lambda Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound brightrimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity (similar to 0.8 L-circle dot) and accretion rate (6.3 x 10(-7) M-circle dot yr(-1)) when compared with other young Class 0 sources (e.g., PACS Bright Red Sources) in the Orion complex. It has slightly larger internal luminosity (0.21 +/- 0.01 L-circle dot) and outflow velocity (similar to 14 km s(-1)) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than an FHSC. Considering its low internal luminosity (0.08 +/- 0.01 L-circle dot) and accretion rate (2.8 x 10(-8) M-circle dot yr(-1)), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency (similar to 0.3%-0.4%) and core formation efficiency (similar to 1%) in PGCC G192.32-11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed owing to stellar feedback.

Herschel observations of the Galactic H ii region RCW 79

Context. Triggered star formation around H ii regions could be an important process. The Galactic H ii region RCW 79 is a prototypical object for triggered high-mass star formation. Aims. We aim to obtain a census of the young stellar population observed at the edges of the H ii region and to determine the properties of the young sources in order to characterize the star formation processes that take place at the edges of this ionized region. Methods. We take advantage of Herschel data from the surveys HOBYS, “Evolution of Interstellar Dust”, and Hi-Gal to extract compact sources. We use the algorithm getsources . We complement the Herschel data with archival 2MASS, Spitzer , and WISE data to determine the physical parameters of the sources (e.g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution. Results. We created the dust temperature and column density maps along with the column density probability distribution function (PDF) for the entire RCW 79 region. We obtained a sample of 50 compact sources in this region, 96% of which are situated in the ionization-compressed layer of cold and dense gas that is characterized by the column density PDF with a double-peaked lognormal distribution. The 50 sources have sizes of ~ 0.1−0.4 pc with a typical value of ~ 0.2 pc, temperatures of ~ 11−26 K, envelope masses of ~ 6−760  M ⊙ , densities of ~ 0.1−44 × 10 5  cm -3 , and luminosities of ~ 19−12 712  L ⊙ . The sources are classified into 16 class 0, 19 intermediate, and 15 class I objects. Their distribution follows the evolutionary tracks in the diagram of bolometric luminosity versus envelope mass ( L bol − M env ) well. A mass threshold of 140  M ⊙ , determined from the L bol − M env diagram, yields 12 candidate massive dense cores that may form high-mass stars. The core formation efficiency (CFE) for the 8 massive condensations shows an increasing trend of the CFE with density. This suggests that the denser the condensation, the higher the fraction of its mass transformation into dense cores, as previously observed in other high-mass star-forming regions.

A mapping study of L1174 with 13CO J=2−1 and 12CO J=3−2: star formation triggered by a Herbig Ae/Be star

We have carried out a comprehensive study of the molecular conditions and star-forming activities in dark cloud L1174 with multi-wavelength data. Mapping observations of L1174 in

N131: A dust bubble born from the disruption of a gas filament

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Follow-Up Observations Toward Planck Cold Clumps with Ground-Based Radio Telescopes

CO

H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION

J=2-1

The discovery based on GLIMPSE data of a protostar driving a bipolar outflow

and

The Properties of Planck Galactic Cold Clumps in the L1495 Dark Cloud

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