Search results for "Stars"

The X-ray Luminosity Distributions of the high-metallicity open cluster Blanco 1

2003

We present X-ray Luminosity Distributions (XLDs) of late-type members (dF, dG, dK, dM) of the Blanco 1 cluster, based on ROSAT-HRI data and new astrometric-photometric membership obtained from the GSC-II project. For the first time we present the XLD of dM stars of this cluster. The high metallicity of Blanco 1 allows us to investigate the role of chemical composition on the coronal emission of late-type stars. Comparison between X-ray Luminosity Distributions of Blanco 1 and Pleiades, NGC 2516 and α  Per suggests a possible metallicity effect in dM stars.

Auvby? survey for Ca II emission stars

1990

During the last two years auvbyβ photometric survey of 85 Ca II emission stars from the Mount Wilson program on stellar activity has been carried out at the Calar Alto Observatory (Almeria, Spain). We present preliminary results for theuvby and β calibrations. Some stars displaying anomalousc1 andm1 indices, with photometric or spectroscopic data from previous studies, are reported. A reddening study for the complete sample is given.

The Hamburg/ESO R-process Enhanced Star survey (HERES): Project Overview, and New r-II Stars

2005

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…

New Limit on Lorentz-Invariance- andCPT-Violating Neutron Spin Interactions Using a Free-Spin-PrecessionHe3-Xe129Comagnetometer

2014

We report on the search for a $CPT$- and Lorentz-invariance-violating coupling of the $^{3}\mathrm{He}$ and $^{129}\mathrm{Xe}$ nuclear spins (each largely determined by a valence neutron) to posited background tensor fields that permeate the Universe. Our experimental approach is to measure the free precession of nuclear spin polarized $^{3}\mathrm{He}$ and $^{129}\mathrm{Xe}$ atoms in a homogeneous magnetic guiding field of about 400 nT using ${\mathrm{LT}}_{C}$ SQUIDs as low-noise magnetic flux detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the colocated spin samples. As a result we obtain…

Precise measurement of the dynamical masses in AB Doradus

2007

AbstractThe radio stars ABDor A and ABDor B (=Rst137B) are the main components of the ABDoradus system. Both stars are double (ABDor A/ABDor C and ABDor Ba/ABDor Bb) and usual targets of astrometric instruments at optical (Hipparcos), infrared (VLT), and radio (VLBI) wavelengths. From a combination of all astrometric data available, we have obtained precise limits to the dynamical mass of both binaries in AB Doradus. The determination of the mass of ABDor C (0.090±0.003 M⊙) is important, since this object constitutes one of the few calibration points used to test theoretical evolutionary models of low-mass young stars. Follow-up observations both in radio (VLBI) and optical wavelengths (VLT…

Phase Reference VLBI Astrometry for Mira-Type Stars

2003

We carried out phase reference VLBI observations at 43 GHz between SiO masers in Mira type variables and adjacent extragalactic continuum source with VLBA. Main aim of this observation is determination of spatial distribution between SiO maser spots at v = 1 and v = 2, J=l→0 transition. Although the standard calibration was successful for each source, the phase reference calibration have not been successful. However, we will determine the absolute positional difference of each SiO maser spot within about 1 milli arcsecond due to the structure effect of reference source if the phase reference VLBI is successful

Modeling the long duration rise phase of a flare detected on the M star TWA 11 B

2009

We present preliminary results from the analysis of a long duration flare that was observed in a serendipitous XMM-Newton detection of the M star CD-39 7717 B (TWA 11 B), member of the young stellar association TW Hya. Only the rise phase (with a duration of ~35 ks) and possibly the flare peak are present in the light-curve. The decay phase was not monitored. The fluorescent iron emission line at 6.4 keV was observed during this event. As far as we are concerned, since TWA 11 B seems to have no disk, this is only the third detection of Fe photospheric fluorescence. During the flare, the X-ray flux increased a factor of ~4. Taking the light curve and the evolution of the hardness ratio into …

Comparison of Hinode/XRT and RHESSI detection of hot plasma in the non-flaring solar corona

2009

We compare observations of the non-flaring solar corona made simultaneously with Hinode/XRT and with RHESSI. The analyzed corona is dominated by a single active region on 12 November 2006. The comparison is made on emission measures. We derive emission measure distributions vs temperature of the entire active region from multifilter XRT data. We check the compatibility with the total emission measure values estimated from the flux measured with RHESSI if the emission come from isothermal plasma. We find that RHESSI and XRT data analyses consistently point to the presence of a minor emission measure component peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI results is withi…

Thermal conduction and modeling of static stellar coronal loops

1993

We have modeled stellar coronal loops in static conditions for a wide range of loop length, plasma pressure at the base of the loop and stellar surface gravity, so as to describe physical conditions that can occur in coronae of stars ranging from low mass dwarfs to giants as well as on a significant fraction of the Main-Sequence stars.