Search results for "Stellar classification"

Stellar physics with the ALHAMBRA photometric system

2011

GREAT-ESF Workshop: Stellar Atmospheres in the Gaia Era 23–24 June 2011, Vrije Universiteit Brussels, Belgium.

Four colour photometry of binary systems

1998

This paper presents new uvby light curves of the detached eclipsing binary CR Cas together with some H measurements. From the analysis of the photometry we have estimated preliminary values for interstellar red- dening and distance, radiative parameters of both compo- nents and an approximation to the geometrical elements of the system. The intrinsic photometric indices are com- patible with spectral types B0.5V + B1V.

A deep catalogue of classical Be stars in the direction of the Perseus Arm: spectral types and interstellar reddenings

2014

We present a catalogue of 247 photometrically and spectroscopically confirmed fainter classical Be stars (13 < r < 16) in the direction of the Perseus Arm of the Milky Way (-1 < b < +4, 120 < l < 140). The catalogue consists of 181 IPHAS-selected new classical Be stars, in addition to 66 objects that were studied by Raddi et al. (2013) more closely, and 3 stars identified as classical Be stars in earlier work. This study more than doubles the number known in the region. Photometry spanning 0.6 to 5 micron, spectral types, and interstellar reddenings are given for each object. The spectral types were determined from low-resolution spectra (lambda / Delta-lambda ~ 800-2000),…

Correlation between the spatial distribution of the circumstellar disks and the massive stars in the open cluster NGC 6611. Compiled catalog and clus…

2006

Context: the observation of young stars with circumstellar disks suggests that the disks are dissipated, starting from the inner region, by the radiation of the central star and eventually by the formation of rocky planetesimals, over a time scale of several million years. It was also shown that strong UV radiation emitted by nearby massive stars can heat a circumstellar disk up to some thousand degrees, inducing the photoevaporation of the gas. This process strongly reduces the dissipation time scale. Aims: we study whether there exists a correlation between the spatial distribution of stars with circumstellar disks and the position of massive stars with spectral class earlier than B5, in …

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

2003

The maximum amplitude (A m a x ) of spot-induced brightness variations from long-term V-band photometry and the ratio L x /L ? o l between X-ray and bolometric luminosities are suitable indicators of the level of magnetic activity in the photosphere and in the corona of late-type stars, respectively. By using these activity indicators we investigate the dependence of coronal X-ray emission on the level of photospheric starspot activity in a homogeneous sample of low mass main sequence field and cluster stars of different ages (IC 2602, IC 4665, IC 2391, a Persei, Pleiades and Hyades). First, the activity-rotation connection at the photospheric level is re-analysed, as well as its dependence…

X-ray variability of NGC 2516 stars in the XMM-Newton observations

2006

We present the characteristics of the X-ray variability of stars in the cluster NGC2516 as derived from XMM-Newton/EPIC/pn data. The X-ray variations on short (hours), medium (months), and long (years) time scales have been explored. We detected 303 distinct X-ray sources by analysing six EPIC/pn observations; 194 of them are members of the cluster. Stars of all spectral types, from the early-types to the late-M dwarfs, were detected. The Kolmogorov-Smirnov test applied to the X-ray photon time series shows that, on short time scales, only a relatively small fraction (ranging from 6% to 31% for dG and dF, respectively) of the members of NGC2516 are variable with a confidence level $\geq$99%…

First results of an Hα based search of classical Be stars in the Perseus Arm and beyond

2013

We investigate a region of the Galactic plane, between 120 <= l <= 140 and -1 <= b <= +4, and uncover a population of moderately reddened (E(B-V) \sim 1) classical Be stars within and beyond the Perseus and Outer Arms. 370 candidate emission line stars (13 <= r <= 16) selected from the INT Photometric H-alpha Survey of the Northern Galactic plane (IPHAS) have been followed up spectroscopically. A subset of these, 67 stars with properties consistent with those of classical Be stars, have been observed at sufficient spectral resolution (Delta_lambda \sim 2 - 4 Angstrom) at blue wavelengths to narrow down their spectral types. We determine these to a precision estimated to be…

The Star Population of Young Open Clusters: A Photometric and Spectroscopic Study

2003

I have determined physical parameters (interstellar reddening, distance, and age) for three young open clusters: h Persei, x Persei, and NGC 1893. I have studied their massive star populations and their formation epochs. I present photometric data for 350 stars in the double open cluster h and x Persei. For both clusters, the distance moduli and reddening are determined to be the same: V0 M p V and E(b y) p . However, the ages for 11.6 0.2 0.42 0.2 the clusters are different. Most stars in h Persei follow the isochrone, although some of the massive stars seem log t p 7.3 younger. By contrast, the stars in x Persei better fit isochrones for (A. Marco & G. Bernabeu 2001, A&A, log t p 7.10–7.1…

On the Age, Spectral Type, Orbit, and Comparison to Evolutionary Models of AB Dor C

2005

The Origin of T Tauri X-ray Emission: New Insights from the Chandra Orion Ultradeep Project

2005

We use the data of the Chandra Orion Ultradeep Project (COUP) to study the nearly 600 X-ray sources that can be reliably identified with optically well characterized T Tauri stars (TTS) in the Orion Nebula Cluster. We detect X-ray emission from more than 97% of the optically visible late-type (spectral types F to M) cluster stars. This proofs that there is no ``X-ray quiet'' population of late-type stars with suppressed magnetic activity. All TTS with known rotation periods lie in the saturated or super-saturated regime of the relation between activity and Rossby numbers seen for main-sequence (MS) stars, but the TTS show a much larger scatter in X-ray activity than seen for the MS stars. S…