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The spectroscopic variability of the Herbig Ae/Be star HD 37806 is analyzed on temporal scales from night-to-night, and over individual nights. The observations were made during November 2012 on the ASP-14 Coude spectrograph installed on the 2.6-m ZTSh telescope at the Crimean Astrophysical Observatory. 40 spectra in the region of the Ha and HeI 5876 lines were obtained over 4 nights. An analysis of the observed variability of the profiles of these lines shows that: (a) the variations in the Ha profiles are well explained under the assumption that they are vibrationally modulated by local azimuthal inhomogeneities in the wind zone and (b) the rapid variability of the HeI 5876 line in the form of standing intensity waves in the region of a red absorbing component is additional evidence of the presence of a magnetosphere in HD37806 that contains local accretion fluxes that rotate rigidly in the star’s magnetic field.

Results are reported from a spectroscopic study of the Herbig Ae/Be star HD 37806 from 2009 through 2017 using high resolution spectrographs at the Crimean Astrophysical Observatory and the OAN SPM Observatory in Mexico. 72 spectra of this object near the Hα, Hβ, HeI 5876 and D NaI lines are analyzed. The following results were obtained: 1. The type of spectral profile of the Hα line can change from P Cyg III to double emission and vice versa over a time scale on the order of a month. 2. Narrow absorption components are observed in the profiles of the Hα and D NaI lines with radial velocities that vary over a characteristic time on the order of a day. 3. On some days, the profiles of the Hβ, HeI 5876, and D NaI lines show signs of accretion of matter to the star with a characteristic lifetime of a few days. A possible interpretation of these phenomena was considered. The transformation of the Hα profile may be related to a change in the outer latitudinal width of the boundary of the wind zone. The narrow variable absorption lines may be caused by the rotation of local azimuthal inhomogeneities in the wind zone owing to the interaction of the disk with the star’s magnetosphere in a propeller regime. Several current theoretical papers that predict the formation of similar inhomogeneous wind structures were examined. It is suggested that the episodes with signs of accretion in the spectral line profiles cannot be a consequence of the modulation of these profiles by the star’s rotation but are more likely caused by sudden, brief changes in the accretion rate. These spectral observations of HD 37806 should be continued in a search for cyclical variability in the spectral parameters in order to identify direct signs of magnetospheric accretion and detect possible binary behavior in this object.

Magellanic Clouds are the nearby galaxies which are ideal to study the properties of metal poor stellar population. In this study, we explore the near-IR properties of optically identified classical Be stars in 19 star clusters in the Magellanic Clouds. From an optically identified sample of 835 Be stars we obtained the J, H, K magnitudes of 389 stars from the IRSF MCPS catalog. Among these, 247 stars (36.4%) are found in 9 clusters in the Large Magellanic Cloud and 142 stars (55.5%) in 10 clusters in the Small Magellanic Cloud. After correcting for reddening, we studied their NIR properties in the (H – K) 0 vs (J – H) 0 diagram. We identified 14 stars with abnormally large near IR excesses, which were removed from the analysis, there by restricting our study to 355 classical Be stars. We propose an extended area in the near-IR (H - K) 0 vs (J - H) 0 diagram as the diagnostic location of Classical Be stars in the Magellanic Clouds. We identified 14 stars to have near-IR excess, higher than those seen in classical Be stars. From the analysis based on spectral energy distribution and luminosity estimate, we found that 8 candidate Be stars may be Herbig Ae/Be stars. We identified a new sample of 6 sgB[e] stars, which when added to the sparse existing sample of 15 sgB[e] stars in the Magellanic Clouds can provide insight to understand the evolutionary link between sgB[e] stars and Luminous Blue variables.

Digital zenith camera system is a highly accurate positioning instrument in geodetic astronomy. It can capture 16 star images in one experiment unit in different azimuthal camera orientations and the stars in each star image should be identified using star catalogue. But the amount of calculation is very large, the efficiency of star identification is low. Now, the improvement of star identification is mainly through updating algorithm. Considering that there exist identical stars in these star images, this paper provides a new method to improve star identification. The star trace is deduced taking the earth rotation and instrument rotation into consideration. The errors of star trace are also analyzed. Then select the same stars that appear in the star images taken in the initial position and after rotating one angle. Using the identical stars instead of star catalogue and the star trace to identify the rest stars, the efficiency will get improved. The analysis of experimental data shows that there are many identical stars in these star images. The appearance of one star can be predicted according to the star trace. The star identification get improved by using the same stars in these star images. And it costs less time to identify the stars in star images, but the precision is approximately equal.

A study of the optical spectra of three Herbig Ae/Be stars is presented: MWC 361,MWC 614, AB Aur. Variations of the equivalent widths, radial velocities, and profiles of spectral lines formed in different regions of the circumstellar environments of these stars are analyzed. The most active spectral variations are observed in the Hα, Hβ, and He I 5876 lines. Other emission lines, such as Si II λλ6347, 6371 Aand [O I] λλ6300, 6363 A, also display variations, but these are much smaller. Interstellar DIBs at λλ5780 and 5797 ˚A were detected for the stars MWC 361 and MWC 614 for the first time. The active processes that are underway in the circumstellar environments of these systems can also reach more distant, outer parts of their circumstellar disks.

We present the results of magnetic field measurements of four chemically peculiar (CP) stars, the members of the Orion stellar association OB1. Observations were carried out with the circular polarization analyzer at the Main Stellar Spectrograph of the 6-m telescope. All the studied stars refer to the subtype of Bp stars with weak helium lines. Canadian astronomer E. F. Borra detected a magnetic field in three of them (HD35456, HD36313, and HD36526) from the Balmer line magnetometer observations. HD35881 was observed for the first time for the purpose to search for a magnetic field. We obtained the following results: HD35456 is a magnetic star with longitudinal field variation range from +300 to +650 G and a period of 4.9506 days; HD35881 is possible a new magnetic star, the longitudinal component of which varies from−1 to +1 kGwith a period of 0.6998 days, however, a small number of lines broadened by rotation does not allow us to conduct measurements more accurately; HD36313 is a binary star with the components similar in brightness, the primary component is a magnetic star with broad lines, the magnetic field of the secondary component (the star with narrow lines) was not detected. Measurements in the Hβ hydrogen line showed the variations of the longitudinal component from −1.5 to +2 kG with a period of 1.17862 days; a strong longitudinal field was detected in HD36526 (from 0 to +3000 G) varying with a rotation period of the star of 3.081 days. In all the cases, we observe considerable discrepancies with the data on magnetic fields of these objects obtained earlier.

The young Herbig Ae star MWC 480 (HD 31648) is one of the comprehensively spectroscopically studied stars in the ultraviolet, optical, and infrared spectral ranges. Using non-LTE modeling of its hydrogen spectrum, we have calculated the contribution to the hydrogen emission from such important regions of the circumstellar environment as the disk wind and the magnetosphere. We have used our own observations of the stellar spectrum performed with the 2.4-m telescope at the Thai National Observatory to quantitatively check our theoretical calculations. In addition, all of the visible and infrared spectra available in the literature have been used for a qualitative comparison. The modeling results have revealed a significant role of the magneto-centrifugal disk wind in the formation of atomic hydrogen emission. The cause of the emission line variability in the spectrum ofMWC 480 is discussed.

This paper continues a study of the photometric activity of UX Ori stars in the optical and near-infrared (JHKLM bands) initiated in 2000. For comparison, the list of program stars contains two Herbig Ae stars that are photometrically quiet in the optical: MWC480 andHD179218. Fadings ofUXOri stars in the optical (V band) due to sporadic increases of the circumstellar extinction are also observed in the infrared (IR), but with decreasing amplitude. Two stars, RR Tau and UX Ori, displayed photometric events when V -band fadings were accompanied by an increase in IR fluxes. Among the two Herbig Ae stars that are photometrically quiet in the optical, MWC 480 proved to be fairly active in the IR. Unlike the UX Ori stars, the variation amplitude of MWC 480 increases from the J band to the M band. In the course of the observations, no deep fadings in the IR bands were detected. This indicates that eclipses of the program stars have a local nature, and are due to extinction variations in the innermost regions of the circumstellar disks. The results presented testify to an important role of the alignment of the circumstellar disks relative to the direction towards the observer in determining the observed IR variability of young stars.

To reproduce the spectral energy distributions (SEDs) of young stellar objects (YSOs), we perform radiative transfer model calculations for the circumstellar dust disks with various shapes and many dust species. For eight sample objects of T Tauri and Herbig Ae/Be stars, we compare the theoretical model SEDs with the observed SEDs described by the infrared space observatory and Spitzer space telescope spectral data. We use the model, CGPLUS, for a passive irradiated circumstellar dust disk with an inner hole and an inner rim for the eight sample YSOs. We present model parameters for the dust disk, which reproduce the observed SEDs. We find that the model requires a higher mass, luminosity, and temperature for the central star for the Herbig Ae/Be stars than those for the T Tauri stars. Generally, the outer radius, total mass, thickness, and rim height of the theoretical dust disk for the Herbig Ae/Be stars are larger than those for the T Tauri stars.

We report the detection of hot H$_{2}$O and OH emission from the Herbig Ae/Be star HD$~101412$ using the Cryogenic Infrared Echelle Spectrograph on the $\textit{Very Large Telescope}$. Previous studies of Herbig Ae/Be stars have shown the presence of OH around some of these sources, but H$_{2}$O has proven more elusive. While marginal water emission has been reported in the mid-infrared, and a few Herbig Ae/Be stars show water emission in the far-infrared, water emission near 2.9 $\mu$m has not been previously detected. We apply slab models to the ro-vibrational OH, H$_{2}$O, and CO spectra of this source and show that the molecules are consistent with being cospatial. We discuss the possibility that the detection of the CO overtone bandhead emission, detection of water emission, and the large line to continuum contrast of the OH lines may be connected to its high inclination and the $\lambda$ Bo\"o nature of this star. If the low abundance of refractories results from the selective accretion of gas relative to dust, the inner disk of HD$~101412$ should be strongly dust-depleted allowing us to probe deeper columns of molecular gas in the disk, enhancing its molecular emission. Our detection of C- and O-bearing molecules from the inner disk of HD$~101412$ is consistent with the expected presence in this scenario of abundant volatiles in the accreting gas., Comment: Accepted for publication in the Astrophysical Journal, 12 pages, 12 figures, 4 tables

Herbig Ae/Be (HAeBe) stars have been classified into Group I or Group II, which were initially thought to be flared and flat disks, respectively. Several Group I sources have been shown to have large gaps, suggesting ongoing planet formation, while no large gaps have been found in the disks of Group II sources. We analyzed the disk around the Group II source, HD 142666, using irradiated accretion disk modeling of the broad-band spectral energy distribution along with the 1.3 millimeter spatial brightness distribution traced by Atacama Large Millimeter and Submillimeter Array (ALMA) observations. Our model reproduces the available data, predicting a high degree of dust settling in the disk, which is consistent with the Group II classification of HD 142666. In addition, the observed visibilities and synthesized image could only be reproduced when including a depletion of large grains out to ~16 au in our disk model, although the ALMA observations did not have enough angular resolution to fully resolve the inner parts of the disk. These results may suggest that some disks around Group II HAeBe stars have cavities of large grains as well. Further ALMA observations of Group II sources are needed to discern how commonly cavities occur in this class of objects, as well as to reveal their possible origins., 11 pages, 3 figures, accepted for publication by The Astrophysical Journal

Herbig Ae/Be stars span a key mass range that links low and high mass stars, and thus provide an ideal window from which to explore their formation. This paper presents VLT/X-Shooter spectra of 91 Herbig Ae/Be stars, HAeBes; the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultra-violet (UV) are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within the Herbig Be mass range., Comment: 29 pages, 19 figures, Accepted for publication in MNRAS

We refined the orbital period of the Herbig Be binary star HD200775 using both new and archive observed data which has been obtained with high-resolution spectrometers at optical wavelengths over 20 years. The new spectroscopic observations were performed with the 1.2-m telescope of the Kourovka Astronomical Observatory of Ural Federal University during 2012–2014 and the 6-m BTA telescope of the Special Astrophysical Observatory in 2013.We show that the period of these observations has a new maximum of activity in 2012 and the following transition of the star to the quiescent state. We confirmed that activity maxima of HD200775, which are characterized by the increase of the Hα equivalent width, appear at intervals of about 3.7 years. A stable orbital period of the system of \(1361_.^d 3 \pm 2_.^d 2\) days was found from radial velocity variations obtained for the He I 5876 A line. It is shown that the radial velocities determined from the Hα emission line and the He I 5876 A absorption line, which is formed in the photosphere of the more massive primary component of the system, are close and change synchronously with time. This synchronization indicates the fact that the major portion of the HD200775 Ha emission originates in the material associated with the more massive component of the system.

We present new results of our photometry for the Herbig Be star HD 52721 obtained from January 16 to March 25, 2013. A new data reduction technique is used. Using this technique, we have also reanalyzed the previous results of our photometry for this object pertaining to the period from March 7 to March 28, 2010. The Be star HD 52721 is known as an eclipsing variable with the period P = 1d. 610. Two photometric minima observed during one period are a peculiarity of its photometric variability. They are separated in phase of the period P by 0.5 and differ from one another in depth by 0m. 04. We have also detected additional minima observed at the phases of maximum brightness. We hypothesize that they can be associated with the existence of local azimuthal inhomogeneities rotating synchronously with the orbital motion of the binary component stars in the circumstellar envelope. When processing our CCD frames, we have applied an efficient CCD-frame rejection method that has allowed the accuracy of observations to be increased considerably. The CCD frames have been further processed using the Apex II software package, which is a universal software platform for astronomical image processing. We justify the need for additional photometric observations of HD 52721 in various color bands to confirm the hypothesis about the existence of azimuthal inhomogeneities in the program binary system and to analyze their physical properties.

We review magnetic-field measurements of nondegenerate stars across the Hertzprung–Russell diagram for main sequence, premain sequence, and postmain sequence stars. For stars with complex magnetic-field morphologies, which includes all G–M main sequence stars, the analysis of spectra obtained in polarized vs unpolarized light provides very different magnetic measurements because of the presence or absence of cancellation by oppositely directed magnetic fields within the instrument’s spatial resolution. This cancellation can be severe, as indicated by the spatially averaged magnetic field of the Sun viewed as a star. These averaged fields are smaller by a factor of 1000 or more compared to spatially resolved magnetic-field strengths. We explain magnetic-field terms that characterize the fields obtained with different measurement techniques. Magnetic fields typically control the structure of stellar atmospheres in and above the photosphere, the heating rates of stellar chromospheres and coronae, mass and angular momentum loss through stellar winds, chemical peculiarity, and the emission of high energy photons, which is critically important for the evolution of protoplanetary disks and the habitability of exoplanets. Since these effects are governed by the star’s magnetic energy, which is proportional to the magnetic-field strength squared and its fractional surface coverage, it is important to measure or reliably infer the true magnetic-field strength and filling factor across a stellar disk. We summarize magnetic-field measurements obtained with the different observing techniques for different types of stars and estimate the highest magnetic-field strengths. We also comment on the different field morphologies observed for stars across the H–R diagram, typically inferred from Zeeman-Doppler imaging and rotational modulation observations

From the theory about the internal structure and stars stability, a relationship for the central temperature of any gaseous star can be obtained.

Effective temperatures and luminosities are calculated for 1,475,921 Tycho-2 and 107,145 Hipparcos stars, based on distances from Gaia Data Release 1. Parameters are derived by comparing multi-wavelength archival photometry to BT-Settl model atmospheres. The 1-sigma uncertainties for the Tycho-2 and Hipparcos stars are +/-137 K and +/-125 K in temperature and +/-35 per cent and +/-19 per cent in luminosity. The luminosity uncertainty is dominated by that of the Gaia parallax. Evidence for infrared excess between 4.6 and 25 microns is found for 4256 stars, of which 1883 are strong candidates. These include asymptotic giant branch (AGB) stars, Cepheids, Herbig Ae/Be stars, young stellar objects, and other sources. We briefly demonstrate the capabilities of this dataset by exploring local interstellar extinction, the onset of dust production in AGB stars, the age and metallicity gradients of the solar neighbourhood and structure within the Gould Belt. We close by discussing the potential impact of future Gaia data releases., 43 pages, 50 figures, accepted MNRAS

We present an NTT/SOFI spectroscopic survey of infrared selected Wolf-Rayet candidates in the Scutum-Crux spiral arm (298 < l < 340, |b| < 0.5). We obtained near-IR spectra of 127 candidates, revealing 17 Wolf-Rayet stars - a ~13% success rate - of which 16 are newly identified here. The majority of the new Wolf-Rayet stars are classified as narrow-lined WN5-7 stars, with 2 broad-lined WN4-6 stars and 3 WC6-8 stars. The new stars, with distances estimated from previous absolute magnitude calibrations, have no obvious association with the Scutum-Crux arm. Refined near-infrared (YHJK) classification criteria based on over a hundred Galactic and Magellanic Cloud WR stars, providing diagnostics for hydrogen in WN stars, plus the identification of WO stars and intermediate WN/C stars. Finally, we find that only a quarter of WR stars in the survey region are associated with star clusters and/or HII regions, with similar statistics found for Luminous Blue Variables in the Milky Way. The relative isolation of evolved massive stars is discussed, together with the significance of the co-location of LBVs and WR stars in young star clusters., 19 pages, accepted for MNRAS, plus 13 pages of supplementary information including near-IR spectral classification of WR stars

We conducted a survey of seven magnetic O and eleven B-type stars with masses above $8M_{\odot}$ using the Very Large Array in the 1cm, 3cm and 13cm bands. The survey resulted in a detection of two O and two B-type stars. While the detected O-type stars - HD 37742 and HD 47129 - are in binary systems, the detected B-type stars, HD 156424 and ALS 9522, are not known to be in binaries. All four stars were detected at 3cm, whereas three were detected at 1cm and only one star was detected at 13cm. The detected B-type stars are significantly more radio luminous than the non-detected ones, which is not the case for O-type stars. The non-detections at 13cm are interpreted as due to thermal free-free absorption. Mass-loss rates were estimated using 3cm flux densities and were compared with theoretical mass-loss rates, which assume free-free emission. For HD 37742, the two values of the mass-loss rates were in good agreement, possibly suggesting that the radio emission for this star is mainly thermal. For the other three stars, the estimated mass-loss rates from radio observations were much higher than those expected from theory, suggesting either a possible contribution from non- thermal emission from the magnetic star or thermal or non-thermal emission due to interacting winds of the binary system, especially for HD 47129. All the detected stars are predicted to host centrifugal magnetospheres except HD 37742, which is likely to host a dynamical magnetosphere. This suggests that non-thermal radio emission is favoured in stars with centrifugal magnetospheres., Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society

Spatially-resolved imaging of Herbig stars and related objects began with HST, but intensified with commissioning of high-contrast imagers on 8-m class telescopes. The bulk of the data taken from the ground have been polarized intensity imagery at H-band, with the majority of the sources observed as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey. Sufficiently many systems have been imaged that we discuss disk properties in scattered, polarized light in terms of groups defined by the IR spectral energy distribution. We find novel phenomena in many of the disks, including spiral density waves, and discuss the disks in terms of clearing mechanisms. Some of the disks have sufficient data to map the dust and gas components, including water ice dissociation products.

A silicate carbon star is a carbon star which shows circumstellar silicate dust features. We col-lect a sample of 44 silicate carbon stars from the literature and investigate the validity of the classification. For some objects, it is uncertain whether the central star is a carbon star. We confirm that 29 objects are verified silicate carbon stars. We classify the confirmed objects into three subclasses based on the evolution phase of the central star. To investigate the effect of the chemical transition phase from O to C, we use the radiative transfer models for the detached silicate dust shells. The spectral energy distributions and the infrared two-color diagrams of the silicate carbon stars are compared with the theoretical model results. For the chemical transition model without considering the effect of a disk, we find that the life time of the silicate feature is about 50 to 400 years depending on the initial dust optical depth.

Early-type stars are well-known to be sources of soft X-rays. However, this high-energy emission can be supplemented by bright and hard X-rays when magnetically confined winds are present. In an attempt to clarify the systematics of the observed X-ray properties of this phenomenon, a large series of Chandra and XMM observations was analyzed, over 100 exposures of 60% of the known magnetic massive stars listed recently by Petit et al. (2013). It is found that the X-ray luminosity is strongly correlated with mass-loss rate, in agreement with predictions of magnetically confined wind models, though the predictions of higher temperature are not always verified. We also investigated the behaviour of other X-ray properties (absorption, variability), yielding additional constraints on models. This work not only advances our knowledge of the X-ray emission of massive stars, but also suggests new observational and theoretical avenues to further explore magnetically confined winds.

The Herbig Ae star PDS2 (CD -53 251) is unusual in several ways. It has a high Galactic latitude, unrelated to any known star-forming region. It is at the cool end of the Herbig Ae sequence, where favorable circumstances facilitate the determination of stellar parameters and chemical abundances. We find $T_{\rm eff} = 6500$ K, and $\log(g) = 3.5$. The relatively low $v\cdot\sin(i) = 12\pm2$ \kms made it possible to use mostly weak lines for the abundances. PDS2 appears to belong to the class of Herbig Ae stars with normal volatile and depleted involatile elements. This pattern is seen not only in $\lambda$ Boo stars, but in some post AGB and RV Tauri stars. The appearance of the same abundance pattern in young stars and highly evolved giants strengthens the hypothesis of gas-grain separation for its origin. The intermediate volatile zinc can violate the pattern of depleted volatiles., Comment: Accepted MNRAS; Online material at http://dept.astro.lsa.umich.edu/~cowley/PDS2.html

We present initial results of the first panoramic search for high-amplitude near-infrared variability in the Galactic Plane. We analyse the widely separated two-epoch K-band photometry in the 5th and 7th data releases of the UKIDSS Galactic Plane Survey. We find 45 stars with \Delta K > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is not yet included in the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions (SEDs) that support classification as Young Stellar Objects (YSOs). This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive pre-main-sequence variables, two of which are deeply embedded. Our results support the recent concept of eruptive variability comprising a continuum of outburst events with different timescales and luminosities, but triggered by a similar physical mechanism involving unsteady accretion. Also, we find what appears to be one of the most variable classical Be stars., Comment: 26 pages, 16 Figures, accepted for publication in MNRAS

NGC 147 and NGC 185, paired satellites of the Andromeda galaxy, possess the same order of mass and analogous structures, but they show different star formation and different amounts of interstellar gas and dust. Therefore, we present the first reconstruction of the star formation history of NGC 147 and NGC 185. Asymptotic Giant Branch stars are highly evolved stars that are brightest in K-band. This maximum K-band magnitude is related to the birth mass of stars. As a result, we have found a 9.9 Gyr old single star formation epoch for NGC 185 followed by relatively continuous star formation. NGC 147, however, has passed through two star formation episodes; one is as old as ∼6 Gyr and the other is as recent as ∼850 Myr. Asymptotic Giant Branch stars are also important dust factories; by fitting Spectral Energy Distributions to observed near and mid infrared data for each star, we were able to measure the dust production rates of individual stars; on order of 10−5M yr −1. Hence, we estimate the total mass entering the interstellar medium to be 1.06 × 10−4M yr−1 and 2.89 × 10−4M yr−1 for NGC 147 and NGC 185.

Axial rotation of a star plays an important role in its evolution, physical conditions in its atmosphere, and appearance of its spectrum. We have analyzed CCD spectra of three stars for which their projected rotational velocity remarkably differs when derived from the Ca II λ 3933 A and MgII λ 4481 A lines. We derived effective temperatures and surface gravities using published uvbyβ photometries and computed synthetic spectra. Comparing observed line profiles of the two lines with the computed ones, we estimated values of v sin i. We also derived radial velocities by means of the cross-correlation function. HD8837 is known to be a shell star with pronounced narrow absorption cores in the Balmer lines as well as in the strong metal lines; however, we do not confirm the emission component in the core of Hβ. HD47964 has been discovered by Hipparcos to be a double. However, in our spectra we do not find traces of the other star. Based on the Hipparcos data, we estimated that the other star would be a main sequence A4 star with an extremely high rotational velocity resulting in wiping out any traces of spectral lines of the companion. HD183986 is known to be a triple star. However, we have found a manifestation of a so far not discovered companion of the component HD183986A and estimated it as a main sequence A5 star having v sin i of about 150 km/s.

By using the 2.16 m telescope of Xinglong Observing Station of National Astronomical Observatories and its high-dispersion spectrograph, the high-dispersion spectroscopic observations of six T Tauri-type stars with weak emission lines (i.e., weak-line T Tauri-type stars, abbreviated as WTTS) were carried out. The lithium abundances of these weak-line T Tauri-type stars are calculated and the relationships of the lithium abundances with the rotation periods as well as the amplitudes of light variations of these stars are discussed. It is found by this study that the lithium abundance for the weak-line T Tauri-type stars with fast rotations tends to be less than that of those with slow rotations. However, for all these weak-line T Tauri-type stars, the lithium abundances have no conspicuous correlation with the amplitudes of light variations of these stars in the V waveband.

In the presently favored picture of star formation, mass is transferred from disk to star via magnetospheric accretion and out of the system via magnetically driven outflows. This magnetically mediated mass flux is a fundamental process upon which the evolution of the star, disk, and forming planetary system depends. Our current understanding of these processes is heavily rooted in young solar analogs, T Tauri Stars (TTS). We have come to understand recently, however, that the higher mass pre-main sequence (PMS) Herbig AeBe (HAeBe) stars have dramatically weaker dipolar fields than their lower mass counterparts. We present our current observational and theoretical efforts to characterize magnetospherically mediated mass transfer within HAeBe star+disk systems. We have gathered a rich spectroscopic and interferometric data set for several dozen HAeBe stars in order to measure accretion and mass loss rates, assess wind and magnetospheric accretion properties, and determine how spectral lines and interferometric visibilities are diagnostic of these processes. For some targets, we have observed spectral line variability and will discuss ongoing time-series spectroscopic efforts.

With the precise, nearly-continuous photometry from the Kepler satellite and the sub-milliarcsecond resolving capabilities of the CHARA Array, astronomy is entering a new age for the imaging and understanding of stellar magnetic activity. We present first results from our Guest Observer Program, where 180 single-epoch surface image reconstructions of KIC 5110407 have revealed differential rotation and hints of magnetic activity cycles based on both spot and flare variations. Analysis of our larger, full dataset will establish in unprecedented detail how surface magnetic activity correlates with stellar age and spectral type. In addition to Kepler work, we have harnessed the power of the world's largest infrared interferometer to “directly” image the spotted surfaces of a few of the closest RS CVn systems, allowing a comparison of contemporaneous Doppler and light-curve inversion imaging techniques.

We present first results of the photometric and spectroscopic investigation of the B1/B2 Herbig star HD52721 performed in 2009–2010 at three observatories: Mountain Astronomical Station (Kislovodsk)—photometry, CrAO (Crimea, Ukraine)—spectroscopy, Observatory San Pedro Martyr (Ensenada, Mexico)—high-resolution echelle-spectroscopy. We have also used photometric data from the ASAS survey for 2003–2009. Our analysis has shown that a) the object is a close binary system with the orbital period of 1.610 days composed of two components of similar spectral type (B1–B2); b) the system is surrounded by the common disk-like envelope containing azimuthal inhomogeneity rotating with the orbital period of the system. We present preliminary estimates of the system parameters and discuss its possible nature.

The results of six years of spectroscopic studies of the Herbig Be star IL Cep (HD216629) are reported. Various spectral parameters of the H alpha and H beta emission lines and those of the He I lambda 5876 absorption feature are found for the first time to have exhibited slow variations in 2006-2011 and to have reached their extrema in 2009-2010. The Na I D1 and D2 lines reproduce, in a weaker form, the H alpha radialvelocity variations. It is suggested that the variations found in the spectrum of the star may be due to the presence of additional bodies in the system.

Photometric and high-resolution spectral data on the Be Herbig star HD 52721 from our earlier article [1] are supplemented by new data obtained with an echelle spectrograph mounted on the 2.1-m telescope at the San Pedro Martir Observatory (Ensenada, Mexico). BVR photometry data obtained during 1987-1998 at the Maidanak Observatory (Uzbekistan) are also examined in more detail. This confirms that the phase light curve for an orbital period P = 1d.610 has two minima with different depths separated in phase by 0.5, and reveals a reddening of the object at the phases of the minima. The profiles of atmospheric He I lines in the 4000-4500 A range are found to be broader, shallower, and more asymmetric at the brightness maximum than at the minimum, as expected in close binary systems. Various factors which may influence the formation of the observed atmospheric line profiles are discussed. The observations confirm the hypothesis of a dense disk shaped gas envelope surrounding the system that makes a significant contribution to its overall brightness and contains a global azimuthal inhomogeneity rotating in synchrony with the orbital motion of the system components. We emphasize the need for new photometric observations of HD 52721 in the region of the atmospheric lines, as well as a continuation of the photometric program, in order to confirm the existence of and to analyze the stable, small variations in the light curve of this object.

We give results of a low-resolution optical spectroscopic study of the bright nebulous stars conforming the tight stellar trapezium embedded in IRAS06548-0815, of the exciting star of IRAS06547-0810, and of the stars associated with reflection nebulae (R-or N-stars) NJ065703.0-081421, NJ065714.1-081016, IRAS06548-0815 D and IRAS06548-0815 G, all objects scarcely observed and apparently pertaining to the dark cloud LDN 1655. Our results given here combined with the corresponding 2MASS near infrared photometry enables us to estimate a photometric distance to LDN1655 of 1.9 kpc and to locate the trapezium stars on the (log Lstar/Lsun, logTeff) or HR diagram in an attempt to disclose about their true nature. The spectroscopy of IRAS06548-0815 revealed two classic T Tauri, two Herbig Ae/Be stars, four weak-line T Tauri stars, and two probable lithium-rich stars. Additionally, we found that the R-star IRAS06547-0810 is excited by a single B1(V) star, that IRAS06548-0815 D is excited by a SpT. B2/B3(V) star, NJ065703.0-081421 and NJ065714.1-081016 are excited by a B3/B4(V) emission star and an A6(V) star, respectively. The brightest near infrared source of the trapezium, IRS1, has an infrared luminosity comparable to a highly reddened O8(V) star (Av of 29m). The second brightest near infrared source of the trapezium, IRAS06548-0815 C is, optically, a single classical T Tauri star of spectral type K4/K5, but is a resolved binary in the 2MASSKs band, both components being of about the same brightness., Submitted to New Astronomy, 18, 42 (2013): 23 pages, 6 Figures

The Herbig Ae/Be stars (HAeBes) allow an exploration of the properties of Pre-Main Sequence(PMS) stars above the low-mass range ($8{\rm\thinspace M_{\odot}}$). This paper is the second in a series exploring accretion in 91 HAeBes with Very Large Telescope/X-shooter spectra. Equivalent width measurements are carried out on 32 different lines, spanning the UV to NIR, in order to obtain their line luminosities. The line luminosities were compared to accretion luminosities, which were determined directly from measurements of an UV-excess. When detected, emission lines always demonstrate a correlation with the accretion luminosity, regardless of detection frequency. The average relationship between accretion luminosity and line luminosity is found to be ${\thinspace L_{\rm acc}}\propto{\thinspace L_{\rm line}}^{1.16 \pm 0.15}$. This is in agreement with the findings in Classical T Tauri stars, although the HAeBe relationship is generally steeper, particularly towards the Herbig Be mass range. Since all observed lines display a correlation with the accretion luminosity, all of them can be used as accretion tracers. This has increased the number of accretion diagnostic lines in HAeBes tenfold. However, questions still remain on the physical origin of each line, which may not be due to accretion., 16 pages, 4 figures

We present observations of solid-state absorption features due to water ice, CO ice, and silicate dust in the spectrum of the bright infrared source (1RS 1) associated with the Herbig-Haro nebula HH 100 in the R Coronae Australis dark cloud. These absorptions are shown to arise predominantly in the molecular cloud rather than in circumstellar matter associated with the infrared source itself, which we deduce to be a premain-sequence star obscured by ∼25 mag of visual extinction. In common with other lines of sight, the spectra indicate the presence of distinct hydrogen-rich (polar) and hydrogen-poor (nonpolar) phases in the ice toward HH 100-IR. The nonpolar phase is dominated by CO. The strength of the solid CO feature at 4.67 μm suggests that as much as ∼40% of all CO in the line of sight may be in the solid phase. Our data show a lack of significant absorption at 4.62 μm that might arise in CN-bearing molecules formed by energetic processing of the mantles. A previous report of structure in the profile of the 3 μm water-ice feature in HH 100-IR that might be attributed to the N-H resonance in condensed ammonia at ∼2.96 μm is not confirmed. The abundance ratio NH3:H2O in the ices is found to be no more than ∼8%, which is probably insufficient to account for the 3.3-3.6 μm "ice-band wing" in terms of ammonium hydrate. However, we propose that the wing might be explained by hydrates containing other bases in addition to ammonia. Further progress is likely to require new laboratory data for appropriate ice mixtures. © 1996. The American Astronomical Sodely. All rights reserved.

The evolution of massive stars is only partly understood. Observational constraints can be obtained from the study of massive stars located in young massive clusters. The ESO Public Survey VISTA Variables in the Via Lactea (VVV) discovered several new clusters hosting massive stars. We present an analysis of massive stars in four of these new clusters. Our aim is to provide constraints on stellar evolution and to better understand the relation between different types of massive stars. We use the radiative transfer code CMFGEN to analyse K-band spectra of twelve stars with spectral types ranging from O and B to WN and WC. We derive the stellar parameters of all targets as well as surface abundances for a subset of them. In the Hertzsprung-Russell diagram, the Wolf-Rayet stars are more luminous or hotter than the O stars. From the log(C/N) - log(C/He) diagram, we show quantitatively that WN stars are more chemically evolved than O stars, WC stars being more evolved than WN stars. Mass loss rates among Wolf-Rayet stars are a factor of 10 larger than for O stars, in agreement with previous findings., paper accepted in New Astronomy

We present the discovery of 816 high amplitude infrared variable stars ($\Delta K_{\rm s} >$ 1 mag) in 119 deg$^2$ of the Galactic midplane covered by the Vista Variables in the Via Lactea (VVV) survey. Almost all are new discoveries and about 50$\%$ are YSOs. This provides further evidence that YSOs are the commonest high amplitude infrared variable stars in the Galactic plane. In the 2010-2014 time series of likely YSOs we find that the amplitude of variability increases towards younger evolutionary classes (class I and flat-spectrum sources) except on short timescales ($$100 days) and 162 short-term variables. Eruptive YSOs and faders tend to have the highest amplitudes and eruptive systems have the reddest SEDs. Follow up spectroscopy in a companion paper verifies high accretion rates in the eruptive systems. Variable extinction is disfavoured by the 2 epochs of colour data. These discoveries increase the number of eruptive variable YSOs by a factor of at least 5, most being at earlier stages of evolution than the known FUor and EXor types. We find that eruptive variability is at least an order of magnitude more common in class I YSOs than class II YSOs. Typical outburst durations are 1 to 4 years, between those of EXors and FUors. They occur in 3 to 6\% of class I YSOs over a 4 year time span., Comment: Accepted for publication in MNRAS, 51 pages, 23 figures

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 $^{13}$CO $J=2-1$ and $^{12}$CO $J=3-2$ were performed using the KOSMA 3-meter telescope. Six molecular cores with masses ranging from 5 to 31 $M_\odot$ and sizes ranging from 0.17 to 0.39 pc are resolved. Large area ahead of a Herbig Be star, HD 200775, is in expanding and core 1 is with collapse signature. Large line widths of $^{13}$CO $J=2-1$ indicate the ubiquity of turbulent motions in this region. Spectra of $^{12}$CO $J=3-2$ prevalently show conspicuously asymmetric double-peaked profiles. In a large area, red-skewed profiles are detected and suggestive of a scenario of global expansion. There is a large cavity around the Herbig Be star HD 200775, the brightest star in L1174. The gas around the cavity has been severely compressed by the stellar winds from HD 200775. Feedbacks from HD 200775 may have helped form the molecular cores around the cavity. Seventeen 2MASS potential young stellar objects were identified according to their 2MASS colour indices. The spatial distribution of the these 2MASS sources indicates that some of them have a triggered origin. All these suggest that feedbacks from a Herbig Ae/Be star may also have the potential to trigger star forming activities., Comment: 13 pages, 10 figures; Accepted for publication in MNRAS

We report the discovery of a bow-shock-producing star in the vicinity of the young massive star cluster NGC 3603 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of this star with Gemini-South led to its classification as O6 V. The orientation of the bow shock and the distance to the star (based on its spectral type) suggest that the star was expelled from the cluster, while the young age of the cluster (~2 Myr) implies that the ejection was caused by a dynamical few-body encounter in the cluster's core. The relative position on the sky of the O6 V star and a recently discovered O2 If*/WN6 star (located on the opposite side of NGC 3603) allows us to propose that both objects were ejected from the cluster via the same dynamical event -- a three-body encounter between a single (O6 V) star and a massive binary (now the O2 If*/WN6 star). If our proposal is correct, then one can "weigh" the O2 If*/WN6 star using the conservation of the linear momentum. Given a mass of the O6 V star of 30 Msun, we found that at the moment of ejection the mass of the O2 If*/WN6 star was 175 Msun. Moreover, the observed X-ray luminosity of the O2 If*/WN6 star (typical of a single star) suggests that the components of this originally binary system have merged (e.g., because of encounter hardening)., Comment: 6 pages, 2 figures. Accepted for publication in MNRAS Letters

An analysis of spectra of the well known Herbig Ae/Be star AB Aur obtained with a high resolution Coude spectrograph (R similar to 20000-25000) installed on the 2.6-m Shejn telescope at the Crimean Astrophysical Observatory (Ukraine) and a medium resolution echelle spectrometer (R similar to 14000) on the 2-m Zeiss telescope at the Shemakha Astrophysical Observatory of the National Academy of Sciences of Azerbaijan yielded an unexpected result. It turns out the the variations in the equivalent widths EW of the HeI 5876 and D NaI emission lines have an inverse correlation (r=-0.67 +/- 0.14 and -0.73 +/- 0.10 according to the data from the CrAO and the ShAO, respectively), while the correlation is direct for the H alpha and HeI 5876 lines (r=+0.68 +/- 0.14 and +0.59 +/- 0.14 according to the data from the CrAO and the ShAO, respectively). The Lafler-Kinman method gives a period P=123.7 days for the variation in the EW of these lines. On phase diagrams plotted for this period, the variations in the EW are sinusoidal, with the variations in EW(HeI) and EW(DNaI) in counterphase, while EW(HeI) and EW(H alpha) are in phase. A possible interpretation of this phenomenon is examined. The need for new spectral observations of AB Aur in order to confirm the observed effects on a larger statistical sample is emphasized.

We present results of multi-epoch (14 nights during 2007–2010) V-band photometry of the cluster NGC 1893 region to identify photometric variable stars in the cluster. The study identified a total of 53 stars showing photometric variability. The members associated with the region are identified on the basis of spectral energy distribution, J − H/H − K two-colour diagram and V/V − I colour–magnitude diagram. The ages and masses of the majority of pre-main-sequence sources are found to be ≲5 Myr and in the range , respectively. These pre-main-sequence sources hence could be T Tauri stars. We also determined the physical parameters like disc mass and accretion rate from the spectral energy distribution of these T Tauri stars. The periods of majority of the T Tauri stars range from 0.1 to 20 d. The brightness of Classical T Tauri stars is found to vary with larger amplitude in comparison to weak line T Tauri stars. It is found that the amplitude decreases with increase in mass, which could be due to the dispersal of discs of massive stars.

Based on high- and medium-resolution spectra, we analyze the population of Be stars in eight young open star clusters. We have found a clear dependence of the relative content of early-type (B0-B3) Be stars on the cluster age. The relative concentration of Be stars of spectral types B0–B3 gradually increases with cluster age, reaching its maximum value of 0.46 in clusters with ages of 12–20 Myr. The almost complete absence of Be stars in older clusters can be easily explained by the fact that B stars leave the main sequence. The few emission objects in clusters with ages of 1–7 Myr are most likely Herbig Be stars. Such a distribution of Be stars in clusters unequivocally points to the evolutionary status of the Be phenomenon. We also briefly consider the causes of this pattern.

The stars in the Chinese star catalogue, Yixiangkaocheng, which were edited by the Jesuit astronomer Kogler in ad 1744 and published in ad 1756, are identified with their counterparts in the Hipparcos catalogue. The equinox of the catalogue is confirmed to be J1744.0. By considering the precession of equinox, proper motions and nutation, the star closest to the location of each star in Yixiangkaocheng, having a proper magnitude, is selected as the corresponding identified star. I identified 2848 stars and 13 nebulosities out of 3083 objects in Yixiangkaocheng, and so the identification rate reached 92.80 per cent. I find that the magnitude classification system in Yixiangkaocheng agrees with the modern magnitude system. The catalogue includes dim stars, whose visual magnitudes are larger than 7, but most of these stars have Flamsteed designations. I find that the stars whose declination is lower than −30° have relatively larger offsets and different systematic behaviour from other stars. This indicates that there might be two different sources of stars in Yixiangkaocheng. In particular, I find that μ1 Sco and γ1 Sgr approximately mark the boundary between two different source catalogues. The observer’s location, as estimated from these facts, agrees with the latitude of Greenwich where Flamsteed made his observations. The positional offsets between the Yixiangkaocheng stars and the Hipparcos stars are 0.6 arcmin, which implies that the source catalogue of stars with δ > −30° must have come from telescopic observations. Nebulosities in Yixiangkaocheng are identified with a few double stars, o Cet (the variable star, Mira), the Andromeda galaxy, ω Cen and NGC6231. These entities are associated with listings in Halley’s Catalogue of the Southern Stars of ad 1679 as well as Flamsteed’s catalogue of ad 1690.

This paper reviews the current state of the problem of magnetism in massive Main Sequence stars. Chemically peculiar Bp stars with enhanced silicon lines and anomalous helium lines in their spectra are shown to be the most promising targets for the observational verification of various mechanisms of the formation and subsequent evolution of magnetic fields in CP stars. A catalog of magnetic Bp stars, containing 125 objects is prepared. Applying different criteria, we compiled a variety of magnetic star samples, which were then used to analyze magnetic fields in objects of different ages. The results of this analysis show that massive stars generally have stronger fields in all the samples studied, and thus confirm earlier results based on smaller star samples. No tight relation is observed and the parameters of individual objects show a very large scatter about the mean relation. The strongest and most complex fields are found in the youngest Bp stars with ages below 30 Myr. Magnetic Bp stars generally rotate slower than normal B-type stars, except for the hottest objects with enhanced helium lines, which have normal rotation velocities. No systematic differences are found between the angular rotation velocities of Bp stars with anomalous helium and silicon lines. We discuss various criteria, which can be used to observationally test the alternative mechanisms of formation and evolution of magnetic fields in CP stars and, in particular, to quantitatively compare not only the magnitudes, but also the topology of fields in objects of different ages.

43 stellar objects with Hα emission are discovered by slitless spectroscopy in a 14’ × 14' area near the nebula GM 2-41 located in the HII region DR 15 at the southern edge of the Cyg OB2 association. Emission is detected for the first time for 30 of these objects. Based on VI and JHK photometric data, the overwhelming majority of these objects are classified as young stellar objects in spectral classes F7-M3 with ages of ~1 Myr. The stars are distributed nonuniformly and form two groups which have the same coordinates as the UCHII regions G0.79 + 0.3 and G79.2 + 0.4.