High-precision UBVRI photometry with a new 50cm telescope at Stará Lesná Pribulla T., Chochol D. Astronomical Institute of the Slovak Academy of Sciences Tatranská Lomnica SLOVAK REPUBLIC

Telescopes at the Astronomical Institute used for the stellar photometry Skalnaté Pleso m a.s.l.: 60/750cm Cassegrain - single- channel photometer, HAMAMATSU R4457P photomultiplier - UBVR photometry Stará Lesná - 810m a.s.l.: (i) 60/750cm Cassegrain - single- channel photometer (high-speed 0.1, 0.01 and 0.001s regime available), EMI 9789QB photomultiplier - UBV photometry

New 50cm telescope at Stará Lesná 50/250cm Newton (observations since February 2003), SBIG ST10- MXE, chip 2174x1536 pixels = 10.9x14.8mm, full-well capacity e -, gain 1.3 e - /ADU 6.8  m pixels, USB interface (full res. download 9s), high QE - U 40%, B - 65%, VR > 80%, I - 30% Filters: UBVRI Johnson system, uvby Str  mgren system, H ,H , [OIII] interference filters planned

Reduction and archiving of the data Reduction of the frames done under the MIDAS environment using procedures written by the first author Magnitudes determined by aperture or PSF fitting Output produced for as many as 50 stars in the field; automatic detection and photometry of all stars on the frame under preparation Large amounts of data thank to fast USB interface & electronics Data archived on CD, log files and coordinates of the frame centers will be searchable via WWW interface (will include also photoelectric observations)

Actual experience Limiting magnitude in the V passband for 30 sec integration: Precision - depends mainly on brightness, aperture, seeing, sky-background level etc.: mag for V = 10mag stars Mount very stable: deviation of the polar axis from the pole < 3’, autoguiding planned Seeing at the observatory site: rather poor = usually 2-6” Instrumental BVRI magnitudes in good agreement with international (  mag  0.03mag for solar-type stars), problems with standardisation of U observations - eff (U) = 3900 ...

Actual experience II Very good time resolution (USB) of data - e.g. for 10s exposures in 4 filters 177 frames/hour, for 20s exposures 118 frames/hour Dark current negatively influences faint objects (<16 mag) in summer (present cooling 35 K under ambient temp.) Problems: positioning of the filters in CWF8 sometimes unreliable, sky flat field negatively influenced by scattered light - low-frequency variations rectified by 2D polynomials

Observational program Active, spotted RS CVn, W UMa and BY Dra stars Symbiotic stars, symbiotic and classical novae Dwarf novae and nova-like objects Peculiar stars - Ap and Am, rapidly-oscillating stars (roAp) Photometry of open and globular clusters Search for the galactic variable stars Search for extrasolar planets (will require changes in mount to cover larger areas of sky) Detection of the optical transients

New CCD multicolour light curves I. Contact binaries Do not require multi-colour observations, except active systems of W subtype (more massive component cooler due to spots) Short period enables to obtain a complete LC in one night for most systems - easy to observe, hard to interpret the data using photometry solely Survey of neglected systems or Hipparcos variables: EE Cet, V921 Her, BI CVn, V344 Lac, V1191 Cyg and active systems: DU Boo, AK Her, TZ Boo etc.

II. Active binaries of the RS CVn type Require multi-colour observations to determine reliable spot temperatures Require high precision  0.003mag to apply eclipse mapping of the components All-sky photometry needed to determine brightness of comparison stars Correct transformation of the data to the international system important for study of long-term changes of brightness Present program SPG: RT And, SV Cam, WY Cnc, XY UMa, CG Cyg, BH Vir, UV Psc, ER Vul (pe photometry)

III. Symbiotic stars, novae Require multi-colour observations to due to the presence of hot and cool component, UB observations reflect flares and outburst of the hot component and accretion disk, RI reflect cool component - pulsations of Mira components Require lower precision for long-term monitoring Correct transformation to the international system complicated by strong emission lines Fast photometry of flare and flickering activity Present program: symbiotic novae V1016 Cyg, V1329 Cyg, HM Sge, PU Vul and RT Ser, symbiotic stars Z And, AX Per, QW Sge, novae V723 Cas, Nova Scuti 2003 (V476 Sct)

Ephemeris for the minimum: E

Future plans Robotisation of the telescope will require changes in equatorial mount (presently Zeiss 7) Automatisation of the dome - step motor will control the movements according to the hour angle, declination and E-W position, step motor will enable to scan larger region of sky - search for variable stars and extra-solar planets - new software under Delphi is being developed Enhanced cooling using water circulation - needed in summer Low-dispersion spectrograph - spectro-photometry of novae & symbiotic stars …larger telescope - the dome would house 100cm telescope on the alt-azimut mount, 80cm telescope on the present mount Remote control of the telescope and camera, will require fast network connection to the building