Discovery of an Optical Jet in the Rosette Nebula： Rosette HH2

We report on the discovery of an optical jet-Rosette HH2-in the Rosette Nebula. The jet system bears unique features for residing at the center of a giant HII region, and its energy source is visible with apparently very low extinction along the line of sight. Unlike most other Herbig-Haro jets, this jet indicates a high-excitation origin, and its extended portion shows a seemingly intact structure, instead of normally a shocked working surface, which is attributed to photoablation.     

The Status of ROSAT X-ray Active Young Stars toward Taurus-Auriga

We present an astrometric study of the candidates of T Tauri stars (TTS)and non-TTS X-ray sources around Tau-Aur, based on the Hipparcos Catalogue andthe ACT Reference Catalogue. The ROSAT selected X-ray sources are found to bea mixed population. A few of them are associated with the Tau-Aur or Orion StarForming Regions (SFR). Some, with distances similar to that of Tau-Aur but withdiscrepant proper motions, are probable or sure Pleiades super-cluster members orother late type young active stars with unresolved nature, more likely to originatein rapidly moving cloudlets, or else having originated from different sites other thanTau-Aur and moved to the present locations. A good many of the non-TTS X-raysources are considered as Hyades cluster members. Some TTS candidates could beforeground pre-main sequence stars or actually young dwarfs not yet depleted oftheir Lithium. Under the hypothesis that the sources we studied are representativeof the ROSAT selected TTS candidates discovered in the outskirts of     

Rotation Periods of Nine ROSAT Selected Solar-Type Stars

We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magni-tude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3days. It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars.     

Studying young stellar populations in G345.5+1.5 molecular cloud

Using different sky surveys, we studied IRAS sources and embedded clusters located in the G345.5+1.5 region. Our analysis comprises multi-wavelength (optical to radio) data, exploited using various methods: photometry, near-infrared spectroscopy for ten stars in the embedded cluster DBS-114, and astrometry. We estimated the main parameters of the embedded stellar populations in the G345.5+1.5 molecular cloud, such as their extent, reddening, age, and mass. We also found a consistent distance value using different approaches. For each studied population, we classified several point objects as early main sequence stars, stars with infrared excess, and class I/II YSOs. For the particular case of DBS 114, our spectral classification revealed four B-type stars, and we used astrometric information from GAIA EDR3. The combination of optical and infrared information revealed an abnormal reddening law in some embedded clusters. Our analysis favored a scenario with a Lyman continuum emission excess at some of the studied stellar populations.     

Statistical Properties of 6.7 GHz Methanol Maser Sources

We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 ≤ [25 - 12] ≤ 1.30 and 1.30 ≤[60 - 12] ≤ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s^-1, and one from about 11 to 20 km s^-1. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks.     

A Study of the Energy Sources of Herbig—Haro Objects

1 INTRODUCTIONHerbig-Haro objects are a kind of semi-sta]c, semi-nebuIa objects associated with star fOrm-ing regions. Although such objects were noticed by Burnham as early as l890s, they did notattract much attention until the late 1940s until their independent rediscovery by Herbig andHaro in NGC 1999. A few years later, these objects were named Herbig-Haro objects fOr thefirst time by Ambartsumian (Reipurth 1997). In the fOllowing half century, the observationand theoretical res…     

Discussion session on star formation,molecular clouds and the interstellar medium

In this panel discussion contributions were made by K. Strom, L. Nordh and H. Zinnecker on the contributions of surveys to the study of star formation regions, by B. Burton on a survey of galactic H I and by E. Dwek on the detection of galactic supernovae by infrared surveys. The contributions of K. Strom, L. Nordh and E. Dwek are summarized here.     

Late-type X-ray Emitting Binaries in the Solar Neighborhood and in Star Forming Regions

We present a spectroscopic and photometric follow-up of binary stars, discovered in a sample of X-ray sources, aimed at a deep characterization of the stellar X-ray population in the solar neighborhood and in Star Forming Regions (SFRs). The sources have been selected from the RasTyc sample, obtained by the cross-correlation between the ROSAT all-sky survey and Tycho catalogues (Guillout et al., 1999). Thanks to the high resolution spectroscopy, we have obtained good radial velocity curves, whose solutions provided us with the mass ratios and minimum masses of the components. We have also obtained an accurate spectral classification with codes specifically developed by us. In addition, we could obtain information on the age of the sources through the Lii-6708 line and on the chromospheric activity level through the Hα line.We show also some results on very young pre-main sequence (PMS) binaries discovered as optical counterparts of X-ray sources in SFRs. The spectroscopic and photometric monitoring has allowed us to determine the orbital and physical parameters and the rotation periods, that are of great importance for testing the models of PMS evolution.     

The stellar populations within theρ Oph cloud cores

We have obtained infrared colors and limiting magnitudes from 1.25–4.8µm for a sample of 26 of the cm continuum radio sources located in the core of the Oph molecular cloud. Their colors demonstrate that the majority of the sources appear to be heavily reddened objects surrounded by circumstellar accretion disks. In these cases the radio emission most likely diagnoses accretion driven energetic outflow phenomena: either ionized winds or possibly synchrotron emission from shocked gas associated with stellar jets.     

A Spitzer survey of young stellar objects in the Rosette Molecular Cloud

We present results from a survey of the Rosette Molecular Cloud (RMC) using both the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) onboard the Spitzer Space Telescope . We have mapped a region of active star formation covering an area approximately 1° by 1.5° including several previously known clusters. Spectral energy distributions (SEDs) fitted to our data combined with that from Two Micron All Sky Survey (2MASS) are used to identify young stellar objects (YSOs) with infrared (IR) excesses. We find that roughly 50 per cent of the sources are forming in clustered environments and identify seven clusters of IR excess sources including four that were previously unknown. We investigate evidence for triggering of star formation due to the ionization front, identified in Brackett-α emission, associated with the young open cluster NGC 2244. Although the position of several of the clusters of IR excess sources are coincident with the ionization front, the bulk of the youngest YSOs are located far from the ionization front, in clusters located along the mid-plane of the cloud. We conclude that although triggering from the H  ii nebula is a possible origin for some of the recent star formation, the majority of the active star formation is occurring in already dense regions of the cloud not compressed by the expansion of the H  ii region.     

A Possible Origin of 6.7 GHz Linear Methanol Maser Sources

LETTERS1 INTRODUCTIONNew1y formed massive stars are obscured by dust, and their clearest signature is oftenat radio frequencies from strong maser emission. Methanol maser emission arises from severaItransitions, the strongest being the 5o -- 61A line at 6.7 GHz, which is also the second strongestGalactic masers of any molecule, first reported by Meaten (1991) and recognized as typical ofClass II masers. CIass II methanol masers are always found in regions of receat massive starfOr…     

After the Supernova: Runaway Stars and Massive X-ray Binary Populations with Metallicity

One of the main pathways by which massive runaways are thought to be produced is by the disruption of a binary system after the supernova (SN) of one of its components. Under such a scenario, the populations of runaway stars in different phases should reflect the input binary population and its evolution. Conversely, if the system stays together after the SN, a High Mass X-Ray Binary (HMXB) may result. We present simulations exploring the behaviour of such runaway and HMXB populations with metallicity, and compare them to observations. As many as two-thirds of massive runaway stars may be produced by supernovae in binaries. Decreasing metallicity lowers the fraction of O stars which are runaway, but increases the Wolf-Rayet runaway fractions and the number of potential HMXBs.     

Spectral energy distribution modelling of southern candidate massive protostars using the Bayesian inference method

Concatenating data from the millimetre regime to the infrared, we have performed spectral energy distribution (SED) modelling for 227 of the 405 millimetre continuum sources of Hill et al. which are thought to contain young massive stars in the earliest stages of their formation. Three main parameters are extracted from the fits: temperature, mass and luminosity. The method employed was the Bayesian inference, which allows a statistically probable range of suitable values for each parameter to be drawn for each individual protostellar candidate. This is the first application of this method to massive star formation.
The cumulative distribution plots of the SED modelled parameters in this work indicate that collectively, the sources without methanol maser and/or radio continuum associations (MM-only cores) display similar characteristics to those of high-mass star formation regions. Attributing significance to the marginal distinctions between the MM-only cores and the high-mass star formation sample, we draw hypotheses regarding the nature of the MM-only cores, including the possibility that the population itself comprises different types of source, and discuss their role in the formation scenarios of massive star formation. In addition, we discuss the usefulness and limitations of SED modelling and its application to the field. From this work, it is clear that within the valid parameter ranges, SEDs utilising current far-infrared data cannot be used to determine the evolution of massive protostars or massive young stellar objects.     

Implementation of New OPAL Tables in Eggleton''''s Stellar Evolution Code

Based on previous works of OPAL, we construct a series of opacity tables for various metallicities Z = 0, 0.000 01, 0.000 03, 0.000 1, 0.000 3, 0.001, 0.004, 0.01, 0.02,0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10 (T/K) ＞ 3.95 and Alexander's for log10 (T/K) ＜ 3.95. At log10 (T/K) - 3.95, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M⊙ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.