We analyze the spatial distributions of young stars in Taurus-Auriga and Upper Sco as determined from the two-point correlation function (i.e. the mean surface density of neighbors). The corresponding power-law fits allow us to determine the fractal dimensions of each association's spatial distribution, measure the stellar velocity dispersions, and distinguish between the bound binary population and chance alignments of members. We find that the fractal dimension of Taurus is D~1.05, consistent with its filamentary structure. The fractal dimension of Upper Sco may be even shallower (D~0.7), but this fit is uncertain due to the limited area and possible spatially-variable incompleteness. We also find that random stellar motions have erased all primordial structure on scales of <0.07 degrees in Taurus and <1.7 degrees in Upper Sco; given ages of ~1 Myr and ~5 Myr, the corresponding internal velocity dispersions are ~0.2 km/s and ~1.0 km/s, respectively. Finally, we find that binaries can be distinguished from chance alignments at separations of <120" (17000 AU) in Taurus and 75" (11000 AU) in Upper Sco. The binary populations in these associations that we previously studied, spanning separations of 3-30", are dominated by binary systems. However, the few lowest-mass pairs (M_prim < 0.3 M_sun) might be chance alignments.
Flare stars were discovered in the late 1940s in the solar vicinity and were named UV Cet-type variables (classical FSs). Among the FSs within 100 pc we search for young stars. For the search we take spectra with sufficient resolution to resolve Lithium at 6707 Åand Calcium at 6718 Åof all the stars. The real young stars are prime targets for the search of extra-solar planets by direct imaging.
We present NIR and MIR observations of eight embedded young stellar groups around Herbig Ae/Be stars (HAEBEs) using archived Spitzer IRAC data and 2MASS data. These young stellar groups are nearby ($\leq$ 1 kpc) and still embedded within their molecular clouds. In order to identify the young stellar objects in our sample, we use the color-color diagram of J - [3.6] vs. Ks - [4.5]. The Spitzer images of our sample show that the groups around HAEBEs, spectral types earlier than B8, are usually associated with bright infrared nebulosity. Within this, there are normally 10 - 50 young stars distrib…
Interaction with possible fallback material, along with the magnetic fields and rotation rates at birth should determine the fates and categories of young neutron stars. This paper addresses some issues related to pure or hybrid accretion models for explaining the properties of young neutron stars.
An age--distance diagram for close-by young isolated neutron stars of different types is introduced and discussed. It is shown that such a diagram can be a useful tool for studying of populations of sources if their detectability strongly depends on age and distance.
The high Galactic longitude end of the Aquila Rift comprises the large Aquila molecular cloud complex, however, few young stars are known to be located in the area, and only one is directly associated with the Rift. In contrast, the Serpens star-forming region at the low Galactic longitude end of the Rift contains hundreds of young stars. We review studies of the raw molecular material and describe searches for young objects in the Aquila clouds. The characteristics of the known young stars and associated jets and outflows are also provided. Finally, we suggest some possible explanations for t…
We now understand how low mass stars evolve through cloud collapse and disc accretion, but whether higher mass stars are also disc accretors is as yet unknown. Spectropolarimetry observations can help in answering this basic question, as they probe the first few stellar radii around young stars.
Preliminary results from spectrophotometric observations of galaxies with very young starbursts are presented. Starburst galaxies with an age of the burst in the range between 3 and 6 Myr have been observed and new detections of Wolf-Rayet galaxies are reported. We discuss the origin of high excitation nebular lines observed in these galaxies and their possible link with the population of Wolf-Rayet stars.
We present $K$-band spectra of the near infrared counterparts to IRS2E and IRS2W which is associated with the ultracompact HII region W51d, both of them embedded sources in the Galactic compact HII region W51 IRS2. The high spatial resolution observations were obtained with the laser guide star facility and Near infrared Integral Field Spectrograph (NIFS) mounted at the Gemini North observatory. The spectrum of the ionizing source of W51d shows the photospheric features NIII (21155 Å) in emission and HeII (21897 Å) in absorption which lead us to classify it as an young O3 type star. We detecte…
We announce the discovery of six Beta Cephei stars and many other variable stars in the young open cluster h Persei (NGC 869). The cluster seems to be very rich in variable B-type stars, similarly to its twin, Chi Persei (NGC 884).
The existence of older stars within a young star cluster can be interpreted to imply that star formation occurs on time scales longer than a free-fall time of a pre-cluster cloud core. Here the idea is explored that these older stars are not related to the star formation process forming the young star cluster but rather that the orbits of older field stars are focused by the collapsing pre-cluster cloud core. Two effects appear: The focussing of stellar orbits leads to an enhancement of the density of field stars in the vicinity of the centre of the young star cluster. And due to the time-depe…
Radial velocity searches for substellar mass companions have focused primarily on stars older than 1 Gyr. Increased levels of stellar activity in young stars hinders the detection of solar system analogs and therefore there has been a prejudice against inclusion of young stars in radial velocity surveys until recently. Adaptive optics surveys of young stars have given us insight into the multiplicity of young stars but only for massive, distant companions. Understanding the limit of the radial velocity technique, restricted to high-mass, close-orbiting planets and brown dwarfs, we began a surv…
We report on the search for planets orbiting 46 nearby young stars performed at the State Observatory of Turingia (TLS) by means of a radial velocity survey. The aim of this program is to test the theories of formation/evolution of planetary systems. For 19(8) stars we can exclude planets with Msini > 1 MJ (5 MJ) and P < 10 days; we find 1 short period binary and 5 stars with long period RV-trend. One good young exo-planet candidate is presented.
The rich star clusters in the Large Magellanic Cloud (LMC) are ideal for studying the process of star formation. Here we focus on the determination of age spreads amongst the massive stars in two young clusters, NGC1818 and NGC1805. We present colour magnitude diagrams (derived from HST data) for these clusters, and discuss the difficulties in age spread determination.
Recent high-resolution observations with the Hubble Space Telescope (HST) reveal that young star clusters of extraordinary luminosity and compactness ("super star clusters") are commonly found in starburst systems. Cluster formation appears to be a dominant mode of star formation in starbursts. The principal properties of the young clusters are summarized. A new ultraviolet HST imaging survey of the central regions of nearby galaxies indicates that young clusters form in a wide range of environments. Circumnuclear star-forming rings, in particular, are richly populated with clusters, and sever…
We present new population synthesis calculations of close young neutron stars. In comparison with our previous investigation we use a different neutron star mass spectrum and different initial spatial and velocity distributions. The results confirm that most of ROSAT dim radioquiet isolated neutron stars had their origin in the Gould Belt. Several tens of young neutron stars can be identified in future in ROSAT data at low galactic latitudes and some of them also can be EGRET unidentified sources.
We present a survey of X-ray emission from young stars in the Sword of Orion star-formation region using XMM-Newton's EPIC detectors. We find over 850 X-ray sources, of which more than 700 have near-infrared counterparts consistent with being young stars. The survey enables statistical investigation of the dependence of X-ray emission properties of young stars on fundamental stellar parameters (mass, rotation, age) and environmental features (circumstellar disk, active accretion, circumstellar absorption), and study of structure size in individual coronae through analysis of large flares.
The recent identification of several groups of young stars within 100 parsecs of the Sun has generated widespread interest. Given their proximity and possible age differences, these systems are ideally suited for detailed studies of disk evolution and planet formation. Here I discuss recent results and prospects for the near-future.
Stellar kinematic groups (SKG) are kinematically coherent groups of stars that share a common origin. We have compiled (Montes et al. 1999; 2000) a sample of late-type stars of previously established members and possible new candidates to different young SKG (Local Association (20 - 150 Myr), Ursa Mayor group (300 Myr), Hyades supercluster (600 Myr), IC 2391 supercluster (35 Myr) and Castor Moving Group (200 Myr)). In order to better understand the origin of these young SKG, and to be able to identify late-type stars members of the classical and the recently identified SKG, we also need to stu…
The aim of this AAS Topical Session was to update the community on the current state of knowledge about the angular momentum evolution of young stars. For newcomers to the subject, the session was intended to provide an introduction and general overview and to highlight emerging issues. For experienced workers in this field, the session provided an opportunity for synthesizing recent developments in observations, theory, and modeling of rotation of young stars and for identifying promising new research directions.
We present detections of the absorption band at 3.53 micron due to solid methanol toward three low-mass young stellar objects located in the Serpens and Chameleon molecular cloud complexes. The sources were observed as part of a large spectroscopic survey of ~40 protostars. This is the first detection of solid methanol in the vicinity of low mass (M <1 Msol) young stars and shows that the formation of methanol does not depend on the proximity of massive young stars. The abundances of solid methanol compared to water ice for the three sources are in the range 15-25% which is comparable to those…
The properties of the brightest resolved stars in an arc that was originally identified by Sun et al. (2005) and is located in the extraplanar regions of M82 are discussed. The stars form an elongated structure that is traced over a projected area of 3.0 x 0.8 kpc. The integrated brightness is M_V ~ -11, while the total stellar mass is between 3 x 10^5 and 2 x 10^6 solar masses. If there is only foreground extinction then the youngest stars have a metallicity Z > 0.008 and an age log(tyears) ~ 7.75; thus, the youngest stars formed at roughly the same time as stars in tidal features that are as…
Spectroscopic studies indicate that gas in the photospheres of young O stars moves at speeds up to the sound speed. We show, using two-dimensional radiation MHD calculations and results from a local linear analysis, that the motions may be due to photon bubble instability if young O stars have magnetic fields.
We present results of the search for variable stars in the field of young open cluster NGC 581. Based on 19 nights of observations, 6 new variable stars were discovered. Two of them turned out to be eclipsing binary systems. Another two detected variable stars are most probably of gamma Dor type. During our observations one of the known Be stars located in our field of view showed irregular variations of brightness, typical for this class of stars. The sixth variable star is a pulsating red giant.
We have identified a candidate 1-2 x 10^5 year old luminous white dwarf in NGC 1818, a young star cluster in the Large Magellanic Cloud. This discovery strongly constrains the boundary mass M_c at which stars stop forming neutron stars and start forming white dwarfs, to M_c > 7.6 Msun.
Brown dwarfs occupy the important region in the mass range between stars and planets. Their existence, ambigious until only recently, and their properties give insight into stellar and planetary formation. We present statistical results of an infrared, coronagraphic survey of young, nearby stars that includes probable companions to three young G-type stars, Gl 503.2 (G2V), HD 102982 (G3V), and Gl 577 (G5V). The companion to Gl 577 is a possible binary brown dwarf, according to evolution ary models. A dynamical determination of the components' masses will be achievable in the near future and be…
Context: Only two planetary systems around old ms-pulsars are currently known. Young radio pulsars and radio-quiet neutron stars cannot be covered by the usually-applied radio pulse timing technique. However, finding substellar companions around these neutron stars would be of great interest -- not only because of the companion's possible exotic formation but also due to the potential access to neutron star physics. Aims: We investigate the closest young neutron stars to search for substellar companions around them. Methods: Young, thus warm substellar companions are visible in the Near Infrar…
The scientific goal of the SACY (Search for Associations Containing Young-stars) was to identify possible associations of stars younger than the Pleiades Association among optical counterparts of the ROSAT X-ray bright sources. High-resolution spectra for possible optical counterparts later than G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. The newly identified young stars present a patchy distribution in UVW an…
Since the first massive planet in a short period orbit was discovered, the question arised how such an object could have formed. There are basically two formation scenarios: migration due to planet-disk or planet-planet interaction. Which of the two scenarios is more realistic can be found out by observing short-period planets of stars with an age between 10E7 and 10E8 yrs. The second aim of the survey is to find out how many planets originally formed, and how many of these are destroyed in the first Gyrs: Do most young, close-in planets evaporate, or spiral into the host stars? In here we rep…
We present a photometric survey aimed to characterize the Be star population of young open clusters. It is found that in these clusters early-type Be stars are more frequent than in the galactic field, and late-type Be stars are scarce or inexistent. We interpret this result as evidence for an evolutionary enhancement of the Be phenomenon towards the end of the main sequence lifetime.
We present 1.4 to 2.5 um integral field spectroscopy of 16 stars in the Braid Nebula star formation region in Cygnus OB7. These data forms one aspect of a large-scale multi-wavelength survey aimed at determining an unbiased estimate of the number, mass distribution, and evolutionary state of the young stars within this one square degree area of the previously poorly studied Lynds 1003 molecular cloud. Our new spectroscopic data, when combined with 2MASS near-IR photometry, provide evidence of membership of many of these objects in the regions pre-main sequence population. We discuss both the c…
We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of ~60 arcmin^2, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (~<5 pc) young (~10-200 Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalog of the candidates including rough approximat…
We report on X-ray emission from members of the recently discovered Tucanae association, a group of stars with youth signatures and similar space motion. The Tucanae association is the nearest known region of recent star formation (at 45 pc) far from molecular clouds. We have made use of the ROSAT Data Archive, and searched for X-rays from Tucanae stars in both ROSAT All-Sky Survey (RASS) and pointed observations. The RASS detection rate for the Tucanae members is 59%. We compare the X-ray luminosity function of the Tucanae association to that of other star forming regions and young star clust…
In our study of M31's globular cluster system with MMT/Hectospec, we have obtained high-quality spectra of 85 clusters with ages less than 1 Gyr. With the exception of Hubble V, the young cluster in NGC 205, we find that these young clusters have kinematics and spatial distribution consistent with membership in M31's young disk. Preliminary estimates of the cluster masses and structural parameters, using spectroscopically derived ages and HST imaging, confirms earlier suggestions that M31 has clusters similar to the LMC's young populous clusters.
Star-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.
In this Work we report, for the extreme starburst in the IR merger NGC 3256: (i) The detection of 4 galactic bubbles, associated with SN explosions.(ii) The first analysis of the spatial distribution of young star clusters (YSC) candidates.(iii) The kinematic study of the ionized gas in the core of of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission line profile could be explained by the presence in the core of YSC with outflow.
The recent availability of accurate proper motion catalogs for millions of stars on the sky (e.g. Tycho-2, UCAC) can benefit projects for which age estimates are needed for stars that are plausibly young (<100 Myr-old) and within a few hundred pc of the Sun. Here I summarize how accurate proper motions have been useful in (1) identifying new, nearby, post-T Tauri star populations, and (2) estimating distances to young field stars which are lacking trigonometric parallax measurements. The later enables the calculation of stellar luminosities and isochronal ages -- two quantities critical for in…
A young neutron star with large spin-down power is expected to be closely surrounded by an e+/- pair plasma maintained by the conversion of gamma-rays associated with the star's polar-cap and/or outer-gap accelerators. Cyclotron-resonance scattering by the e- and e+ within several radii of such neutron stars prevents direct observations of thermal X-rays from the stellar surface. Estimates are presented for the parameters of the Planck-like X-radiation which ultimately diffuses out through this region. Comparisons with observations, especially of apparent blackbody emission areas as a function…
Young star clusters with masses similar to those of classical old globular clusters are observed not only in starbursts, mergers or otherwise disturbed galaxies, but also in normal spiral galaxies. Some young clusters with masses as high as ~10^6 Msun have been found in the disks of isolated spirals. Dynamical mass estimates are available for a few of these clusters and are consistent with Kroupa-type IMFs. The luminosity (and possibly mass-) functions of young clusters are usually well approximated by power-laws. Thus, massive clusters at the tail of the distribution are naturally rare, but a…
We present results of intermediate resolution spectroscopy of 131 optical counterparts to 115 ROSAT All-Sky Survey X-ray sources south of the Taurus-Auriga dark cloud complex. These objects have been selected as candidate young stars from a total of 1084 ROSAT sources in a about 300 square degree area. We identify 30 objects as low-mass PMS stars on the basis of the Li 6708 doublet in their spectrum, a signature of their young age. All these stars have a spectral type later than F7 and show spectral characteristics typical of weak-line and post-T Tauri stars. The presence of young objects seve…
AIMS: The aim of this work is to understand whether there is a difference in the dispersion of discs around stars in high-density young stellar clusters like the Orion Nebula Cluster (ONC) according to the mass of the star. METHODS: Two types of simulations were combined -- N-body simulations of the dynamics of the stars in the ONC and mass loss results from simulations of star-disc encounters, where the disc mass loss of all stars is determined as a function of time. RESULTS: We find that in the Trapezium, the discs around high-mass stars are dispersed much more quickly and to a larger degree…
Star formation in the Local spiral arm in the direction of the Galactic longitudes 132--158 deg is reviewed. Recent star-forming activity in this Milky Way direction is evidenced by the presence here of the Cam OB1 association and dense dust and molecular clouds containing H$α$ emission stars, young irregular variables and infrared stellar objects. The clouds of the Local arm concentrate in two layers at 150-300 pc and at about 900 pc from the Sun. The Perseus arm objects in this direction are at a distance of about 2 kpc.
Recent results from Hubble Space Telescope (HST) have resolved starbursts as collections of compact young stellar clusters. Here we present a photometric catalogue of the young stellar clusters in the nuclear starburst of M82, observed with the HST WFPC2 in Halpha (F656N) and in four optical broad-band filters. We identify 197 young super stellar clusters. The compactness and high density of the sources led us to develop specific techniques to measure their sizes. Strong extinction lanes divide the starburst into five different zones and we provide a catalogue of young super star clusters for …
The simultaneous presence of both the so-called `ultra-fast rotators' and slowly rotating stars among the solar-type stars ($\sim 0.6-1.2 M_{\odot}$) in the same young star clusters has been a puzzle in the field of stellar rotation. No model to date has been able to explain both by a single mechanism intrinsic to the star and questions about the appropriate initial conditions for models often complicate the problem. In this paper, using the same starting conditions for the models that we used in examining the origin of the ultra-fast rotators in young star clusters, we show that the slowest r…
This paper reviews the Chandra deep exposure observations of star forming regions, rho-Ophiuchi, Orion Molecular Clouds 2 and 3, Sagittarius B2 and Monoceros R2. The results are; (1) class I protostars are found to exhibit higher temperature plasma than those of T Tauri stars, (2) heavily absorbed X-rays are discovered from the candidates of class 0 protostars, (3) hard and highly variable X-rays are observed from high-mass young stars, and (4) young brown dwarfs emit X-rays similar to those of low-mass young stars.
N-body simulations have shown that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared Galactic Plane Survey (completed by the Midcourse Space Experiment satellite) to search for bow shocks around a number of young ($\la$ several Myr) clusters and OB associations. We discovered dozens of b…
Galaxy interactions are known to trigger starbursts. The young star clusters formed in mergers may be young globular clusters. The ages of these young star clusters yield the timing of interaction-triggered star formation and provide an important way to reconstruct the history of merging galaxies. Here we present the first results from our investigation into age and metallicity of twelve young clusters in the merging galaxy pair NGC 4676, using spectra from the multi-object Low Resolution Imaging Spectrometer (LRIS) on Keck. For ten clusters, comparison of the Balmer emission lines with model …
We present a new set of evolutionary synthesis models of our GALEV code, specifically developed to include the gaseous emission of presently forming star clusters, in combination with an advanced tool to compare large model grids with multi-color broad-band observations of YSC systems. Tests and first applications are presented.
We present wide-field optical imaging covering the entire neutral hydrogen disc of the Local Group dwarf galaxy NGC 6822. These observations reveal the presence of numerous blue, young stars at large galactocentric radii well beyond R_25. Blue stars are also found that are associated with NGC 6822's companion HI cloud, indicating that star formation was triggered in the companion in the last 10^8 yr. In general, blue stars are present where the HI surface densities reach values > 5 x 10^20 cm^(-2). However, over one-third of the blue stars detected are found at lower surface densities. The you…
The blue star reported in the field of the young LMC cluster NGC1818 by Elson et al. (1998) has the wrong luminosity and radius to be a "luminous white dwarf" member of the cluster. In addition, unless the effective temperature quoted by the authors is a drastic underestimate, the luminosity is much too low for it to be a cluster member in the post-AGB phase. Other possibilities, including that of binary evolution, are briefly discussed. However, the implication that the massive main sequence turnoff stars in this cluster can produce white dwarfs (instead of neutron stars) from single-star evo…
Eleven objects that have been reported as proto-planetary nebula or as young planetary nebulae that show very extended Halpha wings are presented. The extension of these wings is larger than 800 km/s. Data for two symbiotic stars that show this same characteristic is also presented. Raman scattering is the mechanism that best explains the wings in 10 of the PNe and in the 2 symbiotic stars. In the PN IRAS 20462+3416 the wing profile can be explained by very intense stellar wind.
We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using Dusty, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with Dusty, which we can use to calculate the dust temperature in a fie…
Star cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis mod…
We study the systematics of neutron star cooling curves with three representative masses from the most populated interval of the estimated mass distribution for compact objects. The cooling simulations are made in the framework of the nuclear medium cooling (NMC) scenario using different combinations of possible nucleon-nucleon pairing gaps. Possible heating or enhanced cooling mechanisms in the crust are not considered. We define a constraint on the highest possible temperatures for a given age of young neutron stars and show that this limits the freedom of modeling pairing gaps and crust pro…
We review recent advances in our understanding of the innermost regions of the circumstellar environment around young stars, made possible by the technique of long baseline interferometry at infrared wavelengths. Near-infrared observations directly probe the location of the hottest dust. The characteristic sizes found are much larger than previously thought, and strongly correlate with the luminosity of the central young stars. This relation has motivated in part a new class of models of the inner disk structure. The first mid-infrared observations have probed disk emission over a larger range…
Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of such emission is uncertain. Although many or perhaps most recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star. Here we report X-ray imaging spectroscopy observations which reveal a factor ~50 increase in the X-ray flux from a young star that is presently undergoing a spectacular optical/I…
The spectral type is a key parameter in calibrating the temperature which is required to estimate the mass of young stars and brown dwarfs. We describe an approach developed to classify low-mass stars and brown dwarfs in the Trapezium Cluster using red optical spectra, which can be applied to other star-forming regions. The classification uses two methods for greater accuracy: the use of narrowband spectral indices which rely on the variation of the strength of molecular lines with spectral type and a comparison with other previously classified young, low-mass objects in the Chamaeleon I star-…
The Antennae is a pair of late type spirals in the course of merging. The interaction triggered an ongoing strong burst of star formation that also produced a large number of Young Star Clusters (YSCs), many of which seem to be young Globular Clusters (GCs). The observed Luminosity Function of the YSC system is a power-law. We use evolutionary synthesis models for star clusters in comparison with HST WFPC observations of the YSC system in the Antennae to analyse the mass function of this ${\rm \sim 2 \cdot 10^8}$ yr young star cluster system. Properly accounting for age spread effects by indiv…
In the first three papers of this series, about 200 objects in Camelopardalis and the nearby areas of Cassiopeia, Perseus and Auriga were suspected of being pre-main-sequence stars in different stages of evolution. To confirm the evolutionary status of the 15 brightest objects, their far-red range (600--950 nm) spectra were obtained. Almost all these objects are young stars with emissions in H alpha, OI, CaII and P9 lines. The equivalent widths of emission lines and approximate spectral classes of the objects are determined.
Young star clusters in interacting galaxies are often found in groups or clusters of star clusters containing up to 100 single clusters. In our project we study the future fate of these clusters of star clusters. We find that the star clusters merge on time scales of a few dynamical crossing times of the super-cluster. The resulting merger object has similarities with observed dwarf ellipticals (dE). Furthermore, if destructive processes like tidal heating, dynamical friction or interaction with disc or bulge of the parent galaxy are taken into account our merger objects may evolve into object…
We report the detection of three mercury-manganese stars in the Orion OB1 association. HD 37886 and BD-0 984 are in the approximately 1.7 million year old Orion OB1b. HD 37492 is in the approximately 4.6 million year old Orion OB1c. Orion OB1b is now the youngest cluster with known HgMn star members. This places an observational upper limit on the time scale needed to produce the chemical peculiarities seen in mercury-manganese stars, which should help in the search for the cause or causes of the peculiar abundances in HgMn and other chemically peculiar upper main sequence stars.
