Solitary A0V X-ray star

A single or solitary A0V X-ray star is significant because it suggests that a coronal cloud occurs very near to or around the star which is not expected from theories involving large amounts of convection as in the Sun or radiatively driven stellar winds as in visual spectral type O- and early B-type stars. Rotational velocities of A0V stars are likely to range widely rather than be concentrated in one band.
109 Virginis
Using differential Stroemgren uvby photometric observations from the Four College Automated Photoelectric Telescope, no evidence for variablility within a season of observation has been found for 109 Virginis.
Vega has been rejected as a primary standard because it is a peculiar star (pole-on rapid rotator with a debris disk) and historically displayed variability. Instead, 109 Virginis is taken as the primary visible standard.
On July 27, 1977, at 05:41:48.1 UTC, an Aerobee 350 or boosted Black Brant launched from White Sands Missile Range using Vega as a reference by its star tracker to update its position while maneuvering between X-ray targets automatically observed Vega with its X-ray telescope for 4.8 s. The quantity of detected photons in the band 0.15-0.80 keV corresponds to an X-ray luminosity L<sub>x</sub> ≈ 3 x 10 erg s .
That Vega is regarded as an X-ray source rests on one 4.8 s star-tracking observation by one sounding rocket flight carrying an X-ray detector flown on many flights that yields trustworthy results. In order to appreciate the magnitude of this difficulty, consider the Sun.
Delta Sculptoris
Although delta Sculptoris is a triple star system, the primary component, delta Sculptoris A, is a white A0V main sequence dwarf, where component B is more than 175 astronomical units (AU) away. The third component is even further at over 3200 AU. Delta Sculptoris A is ROSAT X-ray source 1RXS J234854.7-280751. It is approximately 143 light-years away.
HR 853
HR 853 is visual spectral type A0V and X-ray source 1RXS J025048.0-395607. It is a solitary star with a trigonometric parallax of 11.34 mas (88.18 parsecs, 287.6 light-years).
Of the 5572 A0V type stars in the SIMBAD database, thirty-one are known X-ray sources.
KS Orionis
KS Ori is an Orion variable star of spectral type A0V in the Orion Nebula. It has been detected several times by the Chandra X-ray Observatory as an X-ray source.
Stellar wind
Given the lack of a significant outer convection zone, theory predicts the absence of a magnetic dynamo in earlier A stars. A-type stars do not have strong stellar winds relative to their luminosity, so that stellar wind drag is generally much less effective than Poynting-Robertson (P-R) drag and may not contribute much toward dust removal around A-type stars.
In early stars of spectral type O and B, shocks developing in unstable winds are the likely source of X-rays.
109 Virginis has a rotational velocity of 334 km s which is higher than Vega. A0V star HR 7384 is an X-ray source detected by the Einstein Observatory and ROSAT, yet its rotational velocity is 190 km s .<ref nameDworetsky/> Per SIMBAD both stars HR 6974 and HR 8231 are solitary spectral type B9.5V with rotational velocities of 70 and 190 km s and are X-ray sources.<ref nameDworetsky/>

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