We obtained the first VRI CCD light curves of the short-period contact eclipsing binary AQ Boo, which was observed on March 22 and April 19 in 2014 at Xinglong station of National Astronomical Observatories, and on January 20, 21 and February 28 in 2015 at Kunming station of Yunnan Observatories of Chinese Academy of Sciences, China. Using our six newly obtained minima and the minima that other authors obtained previously, we revised the ephemeris of AQ Boo. By fitting the O-C (observed minus calculated) values of the minima, the orbital period of AQ Boo shows a decreasing tendency dP/dt=-1.47(0.17)x10^-17^day/year. We interpret the phenomenon by mass transfer from the secondary (more massive) component to the primary (less massive) one. By using the updated Wilson & Devinney (1971ApJ...166..605W) program, we also derived the photometric orbital parameters of AQ Boo for the first time. We conclude that AQ Boo is a near contact binary with a low contact factor of 14.43%, and will become an over-contact system as the mass transfer continues.
We study the distribution of galaxies and galaxy clusters in a 10{deg}x6{deg} field in the Aquarius region. In addition to 63 clusters in the literature, we have found 39 new candidate clusters using a matched-filter technique and a counts-in-cells analysis. From redshift measurements of galaxies in the direction of these cluster candidates, we present new mean redshifts for 31 previously unobserved clusters, while improved mean redshifts are presented for 35 other systems.
We present spectroscopic and photometric data for 920 galaxies selected in 68 fields of the Aquarius Cluster Catalog. Typically, the 15 brightest candidate members with magnitudes in the range 16<b_J_<21 were selected for observations, and ~71% turn out to be cluster members. Using the new redshift determinations, we assign galaxies to groups and clusters, and by including data from the literature we calculate systemic velocities and velocity dispersions for 74 clusters, each with redshifts measured for at least six individual galaxies.
We have imaged the portion of the Shapley Concentration core surrounding the cluster A3556 at wavelengths of 36cm with the Molonglo Observatory Synthesis Telescope (MOST), and at 22 and 13cm with the Australia Telescope Compact Array (ATCA). We have defined a radio sample of 112 radio sources at 22cm. Cross-correlation with optical catalogues allowed the identification of 29 radio sources, nine of which belong to A3556. The radio and optical properties of A3556 have been studied in detail. Two extended radio sources are associated with cluster members, i.e. a narrow-angle-tail source located at a projected distance of 0.06R_A_ from the centre, possibly in the late stages of its existence, and a wide-angle-tail source at the periphery of the cluster. We also performed a statistical analysis of the cluster properties. The optical luminosity function shows that the cluster has an excess of bright optical galaxies. In agreement with well-established results, we found that the probability of radio emission increases for brighter galaxies. Furthermore, our radio luminosity function and those obtained for elliptical galaxies located in different environments (poor groups and rich clusters) are very similar, implying that the peculiar dynamical state of A3556 has no influence on the radio emission properties of the cluster galaxies.
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.
