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Corrected mu_delta for Stars of Hipparcos Catalogue from Independent Latitude Observations over Many Decades

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Author(s): Damljanovic, G. | Milic, I. S.

Journal: Serbian Astronomical Journal
ISSN 1450-698X

Volume: 182;
Start page: 35;
Date: 2011;
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Keywords: Astrometry | Reference systems

ABSTRACT
During the last century, there were many so-calledindependent latitude (IL) stations with the observations whichwere included into data of a few international organizations(like Bureau International de l'Heure -- BIH, International PolarMotion Service -- IPMS) and the Earth rotation programmes fordetermining the Earth Orientation Parameters -- EOP. Because ofthis, nowadays, there are numerous astrometric ground--basedobservations (made over many decades) of some stars included inthe Hipparcos Catalogue (ESA 1997). We used these latitude datafor the inverse investigations -- to improve the proper motions indeclination $mu_{delta}$ of the mentioned Hipparcos stars. Wedetermined the corrections $Deltamu_{delta}$ and investigatedagreement of our $mu_{delta}$ and those from the cataloguesHipparcos and new Hi-ppar-cos (van Leeuwen 2007). To do this weused the latitude variations of 7 stations (Belgrade,Blagoveschtschensk, Irkutsk, Poltava, Pulkovo, Warsaw andMizusawa), covering different intervals in the period 1904.7 --1992.0, obtained with 6 visual and 1 floating zenith telescopes(Mizusawa). On the other hand, with regard that about two decadeshave elapsed since the Hi-ppar-cos ESA mission observations (theepoch of Hi-ppar-cos catalogue is 1991.25), the error ofappa-rent places of Hipparcos stars has increased by nearly 20mas because of proper motion errors. Also, the mission lasted lessthan four years which was not enough for a sufficient accuracy ofproper motions of some stars (such as double or multiple ones).Our method of calculation, and the calculated $mu_{delta}$ forthe common IL/Hipparcos stars are presented here. We constructedan IL catalogue of 1200 stars: there are 707 stars in the firstpart (with at least 20 years of IL observations) and 493 stars inthe second one (less than 20 years). In the case of $mu_{delta}$of IL stars observed at some stations (Blagoveschtschensk,Irkutsk, Mizusawa, Poltava and Pulkovo) we find the formal errorsless than the corresponding Hipparcos ones and for some of them(stations Blagoveschtschensk and Irkutsk) even less than the newHipparcos ones.
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