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HD 190946


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The X-Ray Emission of A-Type Stars
From X-ray images in the ROSAT public archives, we determine soft X-rayfluxes, or flux upper limits, for 74 A-type stars, which have beenobserved during deep integrations with the PSPC. Nine supposedly single,late A stars (0.20 < B-V < 0.35) are found to coincide with X-raysources. The X-ray luminosities we infer for these stars range fromlevels comparable to the Active Sun, at log L_x ~27.6, to much brighteremission levels similar to those observed for active late-type binarysystems, near log L_x ~30.1. Another 10 sources are identified withearly A stars (0.0 < B-V < 0.2). Five of these are confirmeddouble stars, the rest are ostensibly single. The maximum luminosity wedetect in the early A stars, log L_x = 30.1, is 3.5 orders of magnitudebrighter than the X-ray upper limits for the nondetected stars.Additional study, including radial velocity monitoring and/or opticalinterferometry, will be needed to determine whether the putativelysingle X-ray emitting stars are in fact single, or whether theiremission is produced entirely or in part by unknown or unresolved binarycompanions. The level of X-ray emission associated with chemicallynormal, single A stars thus far appears to be uncorrelated with anyobvious stellar property, including the rotation rate, which is known togreatly influence the dynamo activity and the X-ray emission levels oflower mass stars. (SECTION: Stars)

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Osservazione e dati astrometrici

Costellazione:Volpetta
Ascensione retta:20h06m40.19s
Declinazione:+22°42'43.1"
Magnitudine apparente:7.878
Distanza:869.565 parsec
Moto proprio RA:0.1
Moto proprio Dec:-6.8
B-T magnitude:7.822
V-T magnitude:7.874

Cataloghi e designazioni:
Nomi esatti
HD 1989HD 190946
TYCHO-2 2000TYC 2154-3733-1
USNO-A2.0USNO-A2 1125-15097497
HIPHIP 99058

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