We present UBV I CCD photometry of the stellar contents and globular cluster(GC) candidates in the spiral galaxy NGC 300 in the Sculptor group. Color-magnitude diagrams for 18 OB associations having more than 30 member stars are presented. The slope of the initial mass function for the bright stars in NGC 300 is estimated to be Γ = −2.6±0.3. Assuming the distance to NGC 300 of (m−M)0 = 26.53± 0...

We present UBV I CCD photometry of the stellar contents and globular cluster(GC) candidates in the spiral galaxy NGC 300 in the Sculptor group. Color-magnitude diagrams for 18 OB associations having more than 30 member stars are presented. The slope of the initial mass function for the bright stars in NGC 300 is estimated to be Γ = −2.6±0.3. Assuming the distance to NGC 300 of (m−M)0 = 26.53± 0...

We present U, B, V, I broad-band, 6200 Å TiO medium-band and Hα narrow-band photometry of the Orion Nebula Cluster (ONC) obtained with the WFI imager at the ESO/MPI 2.2 telescope at La Silla Observatory. The nearly-simultaneous observations, cover the entire ONC in a field of about 34× 34 arcmin. They enable us to determine stellar colors avoiding the additional scatter in the photometry induce...

We analyze very deep HST, VLT and Spitzer photometry of galaxies at 2 < z < 3.5 in the Hubble Deep Field South. The sample is selected from the deepest public K-band imaging currently available. We show that the rest-frame U−V vs V −J color-color diagram is a powerful diagnostic of the stellar populations of distant galaxies. Galaxies with red rest-frame U − V colors are generally red in restfr...

We intend to use the restored HST to study age structure and chemical evolution of the stellar population at the center of the LMC. To obtain the necessary observational parameters, Strömgren photometry is planned using the Planetary Camera. To study the reduction techniques needed, a set of simulated PC images have been made. The stellar density in the images is based on an extrapolated lumino...

We briefly describe a method of obtaining relative intrinsic stellar parameters, such as absolute magnitudes and colors from the light curves of fundamental mode RR Lyrae (RRab) stars. Absolute stellar parameters of double-mode variables (Cepheids and RR Lyrae stars) can be computed from their periods and intrinsic colors combined with stellar atmosphere and pulsation models. By using these two...

Stellar image matching allows to verify if a given pair of images belongs to the same stellar object/area, or knowing that they correspond to the same sky area, to verify if there are some changes between them due to an stellar event (supernova event, changes in the object position, etc). Some applications are stellar photometry, telescope tracking and pointing, robot telescopes, and sky monito...

We present synoptic optical photometry of HD 189733, the chromospherically active parent star of one of the most intensively studied exoplanets. We have significantly extended the timespan of our previously reported observations and refined the estimate of the stellar rotation period by more than an order of magnitude: P = 11.953± 0.009 days. We derive a lower limit on the inclination of the st...

Using optical/near-IR broadband photometry together with Hα emission line data, we attempt to constrain the star formation histories, ages, total stellar masses and stellar mass-to-light ratios for a sample of extremely blue low surface brightness galaxies. We find that, under standard assumptions about the stellar initial mass function, the Hα equivalent widths of these objects appear inconsis...

We examine the correlation between stellar metallicity and the presence of shortperiod planets. It appears that approximately 1 % of dwarf stars in the solar neighborhood harbor short-period planets characterized by near-circular orbits and orbital periods P < 20 days. However, among the most metal-rich stars (defined as having [Fe/H] > 0.2 dex), it appears that the fraction increases to 10%. U...