Query : 2002A&A...393L..33V

2002A&A...393L..33V - Astronomy and Astrophysics, volume 393, L33-36 (2002/10-2)

Astrometry of the stellar image of U Her amplified by the circumstellar 22 GHz water masers.


Abstract (from CDS):

The 22GHz H2O masers in the circumstellar envelope of the Mira variable star U Her have been observed with MERLIN using a phase referencing technique to determine accurate astrometric positions. The positions were compared with the optical positions obtained with the Hipparcos satellite to an accuracy of 18 mas. The absolute radio position of the brightest H2O maser spot is found to match the optical position, indicating that this spot is the stellar image amplified by the maser screen in front of it. The occurrence of an amplified image in the 22GHz maser can be used to accurately determine the positions of the H2O with respect to the star as well as with respect to the SiO and OH masers. Our observations seem to indicate that the star is not in the centre of the distribution of maser spots, which has been interpreted as a ring.

Abstract Copyright:

Journal keyword(s): masers - stars: circumstellar matter - stars: individual: U Her - stars: AGB and post-AGB - techniques: interferometric - astrometry

CDS comments: J1628+214 = JVAS J1630+2131, J1635+1831 = JVAS J1635+1831, J1619+2247 = VCS1 J1619+2247.

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 V* W Hya Mi* 13 49 02.0018313132 -28 22 03.532006894   8.97 7.70     M7.5-9e 635 0
2 V* U Her OH* 16 25 47.4719383584 +18 53 32.863368084 8.85 8.23 6.70     M6.5-8+e 537 1
3 NVSS J163011+213134 Rad 16 30 11.23054976 +21 31 34.3081139           ~ 20 1
4 QSO B1633+186 QSO 16 35 39.1581698904 +18 31 03.697636296     17.0     ~ 23 1

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