We have performed a search for variable stars in the dwarf irregular galaxy NGC 6822 using wide-field multi-epoch VI photometry down to a limiting magnitude of ~22. A part from the Cepheid variables in this galaxy already reported in an earlier paper by Pietrzynski et al. (2004AJ....128.2815P), we have found 1019 "non-periodic" variable stars, 50 periodically variable stars with periods ranging from 0.12 to 66 days and 146 probably periodic variables. Twelve of these stars are eclipsing binaries and fifteen are likely new, low-amplitude Cepheids.
For the first time, we have detected Cepheid variables in the Sculptor Group spiral galaxy NGC 7793. From wide-field images obtained in the optical V and I bands on 56 nights in 2003-2005, we have discovered 17 long-period (24-62 days) Cepheids whose periods and mean magnitudes define tight period-luminosity relations. We use the (V-I) Wesenheit index to determine a reddening-free true distance modulus to NGC 7793 of 27.68+/-0.05mag (internal error) +/-0.08mag (systematic error).
We present near-infrared J- and K-band photometry of 77 Cepheid variables in the Local Group galaxy NGC 3109. Combining our data with the previously published optical V- and I-band photometry of Cepheids in this galaxy, we derive an accurate distance and interstellar reddening toward NGC 3109.
We have obtained mosaic images of NGC 3109 in the V and I bands on 74 nights, spanning approximately 1yr. From these data, we have conducted an extensive search for Cepheid variables over the entire field of the galaxy, resulting in the discovery of 113 variables with periods ranging from 3.4 to 31.4days. In this sample, 76 Cepheids, including many long-period variables, were not known before. For the previously known 45 Cepheids in this galaxy, our data proved that reported periods were wrong for 14 objects; for nearly all other previously known Cepheid variables, we were able to significantly improve on the periods.
We have detected, for the first time, Cepheid variables in the Sculptor Group SB(s)m galaxy NGC 55. From wide-field images obtained in the optical V and I bands during 77 nights in 2002-2003, we have found 143 Cepheids with periods ranging from 5.6 to 175.9 days; 133 of these objects have periods longer than 10 days, making NGC 55 to date the galaxy with the largest known number of long-period Cepheids in the Sculptor Group.
We have conducted an extensive wide-field imaging survey for Cepheid variables in the Local Group irregular galaxy WLM. From data obtained on 101 nights, we have discovered 60 Cepheids, which include 14 of the 15 Cepheid variables previously detected by Sandage and Carlson. Our Cepheid survey in WLM should be practically complete down to a period of 3-days. Importantly, we have found for the first time a long-period Cepheid (P=54.2-days) in this galaxy, alleviating the problem that WLM with its many blue, massive stars does not contain Cepheids with periods longer than about 10-days.
We have obtained deep images in the near-infrared J and K filters of four fields in the Sculptor group spiral galaxy NGC 55 with the ESO VLT and ISAAC camera. For 40 long-period Cepheid variables in these fields, which were recently discovered by Pietrzyski et al., we have determined mean J and K magnitudes from observations at two epochs, and derived distance moduli from the observed period-luminosity (PL) relations in these bands.
We have conducted a survey for Cepheid variables in the Sculptor group spiral NGC 300. Based on observations obtained with the Wide-Field Camera at the 2.2m ESO/MPI telescope at the La Silla observatory in Chile during 29 nights spread over a 5.3 month interval. The telescope was equipped with the ESO mosaic Wide-Field Camera (WFI) consisting of eight 2048x4098 pixel arrays. The CCDs were separated by gaps of 23.8" and 14.3" in right ascension and declination, respectively. The total field of view was about 34'x33' with a scale of 0.238"/pixel. 117 Cepheids and 12 Cepheid candidates were found, which cover the period range from 115 to 5.4 days. We present a catalog that provides equatorial coordinates, period, time of maximum brightness, and intensity mean B and V magnitudes for each variable, and we show phased B and V light curves for all the Cepheids found. We also present the individual B and V observations for each Cepheid in our catalog. During our search we rediscovered all 18 previously known Cepheids and confirmed the Cepheid nature of three Cepheid candidates from the previous photographic survey of Graham (1984AJ.....89.1332G). Star V4 in Graham's list (1984AJ.....89.1332G), classified by him as an eclipsing binary, turns out to be another Cepheid. We find very good agreement between our photometry and that obtained by Freedman et al. (1992ApJ...396...80F) from ground-based CCD data for common stars. Using the earlier data together with our new data, we were able to significantly improve the periods for 15 Cepheids in our sample.
We have obtained mosaic images of NGC 6822 in the V and I bands on 77 nights. From these data, we have conducted an extensive search for Cepheid variables over the entire field of the galaxy, and we have found 116 such variables with periods ranging from 1.7 to 124 days. We used the long-period (>5.6 days) Cepheids to establish the period-luminosity (PL) relations in V, I, and in the reddening-independent Wesenheit index, which are all very tightly defined.
We have measured near-infrared magnitudes in the J and K bands for 56 Cepheid variables in the Local Group galaxy NGC 6822 with well-determined periods and optical light curves in the V and I bands. Using the template light-curve approach of Soszyski and coworkers (2005PASP..117..823S), accurate mean magnitudes were obtained from these data, which allowed us to determine with unprecedented accuracy the distance to NGC 6822 from a multi-wavelength period-luminosity solution in the VIJK bands.
