The ARAUCARIA project. Discovery of Cepheid Variables in NGC 300 from a Wide-Field Imaging Survey

Based on observations of NGC 300, obtained with the Wide-Field Camera at the 2.2 m ESO/MPI telescope during 29 nights spread over a 5.3 month interval, 117 Cepheids and 12 Cepheid candidates were found which cover the period range from 115 to 5.4 days. We present a catalog which 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. We find very good agreement between our photometry and that obtained by Freedman et al. from ground-based CCD data for common stars. The Cepheids delineate the spiral arms of NGC 300, and a couple of them were detected very close to the center of the galaxy. From the color-magnitude diagram of NGC 300 constructed from our data, we expect that our Cepheid detection is near-complete for variables with periods larger than about 10 days. We present plots of the PL relations in the B and V bands obtained from our data, which clearly demonstrate the presence of a Malmquist bias for periods below about 10 days. A thorough discussion of the distance to NGC 300 will be presented in a forthcoming paper which will include the analysis of photometry in longer-wavelength bands.Comment: 26 pages, Latex. Astronomical Journal in pres

Direct Distances to Cepheids in the Large Magellanic Cloud: Evidence for a Universal Slope of the Period-Luminosity Relation up to Solar Abundance

We have applied the infrared surface brightness (ISB) technique to derive distances to 13 Cepheids in the LMC which span a period range from 3 to 42 days. From the absolute magnitudes of the variables calculated from these distances, we find that the LMC Cepheids define tight period-luminosity relations in the V, I, W, J and K bands which agree exceedingly well with the corresponding Galactic PL relations derived from the same technique, and are significantly steeper than the LMC PL relations in these bands observed by the OGLE-II Project in V, I and W, and by Persson et al. in J and K. We find that the tilt-corrected true distance moduli of the LMC Cepheids show a significant dependence on period, which hints at a systematic error in the ISB technique related to the period of the stars. We identify as the most likely culprit the p-factor which converts the radial into pulsational velocities; our data imply a much steeper period dependence of the p-factor than previously thought, and we derive p=1.58 (+/-0.02) -0.15 (+/-0.05) logP as the best fit from our data, with a zero point tied to the Milky Way open cluster Cepheids. Using this revised p-factor law, the period dependence of the LMC Cepheid distance moduli disappears, and at the same time the Milky Way and LMC PL relations agree among themselves, and with the directly observed LMC PL relations, within the 1 sigma uncertainties. Our main conclusion is that the previous, steeper Galactic PL relations were caused by an erroneous calibration of the p-factor law, and that there is now evidence that the slope of the Cepheid PL relation is independent of metallicity up to solar metallicity, in both optical, and near-infrared bands.Comment: ApJ accepte

Distances to six Cepheids in the LMC cluster NGC1866 from the near-IR surface-brightness method

We derive individual distances to six Cepheids in the young populous star cluster NGC1866 in the Large Magellanic Cloud employing the near-IR surface brightness technique. With six stars available at the exact same distance we can directly measure the intrinsic uncertainty of the method. We find a standard deviation of 0.11 mag, two to three times larger than the error estimates and more in line with the estimates from Bayesian statistical analysis by Barnes et al. (2005). Using all six distance estimates we determine an unweighted mean cluster distance of 18.30+-0.05. The observations indicate that NGC1866 is close to be at the same distance as the main body of the LMC. If we use the stronger dependence of the p-factor on the period as suggested by Gieren et al. (2005) we find a distance of 18.50+-0.05 (internal error) and the PL relations for Galactic and MC Cepheids are in very good agreement.Comment: Presented at the conference "Stellar Pulsation and Evolution" in Monte Porzio Catone, June 2005. To appear in Mem. Soc. Ast. It. 76/

Evidence for a Universal Slope of the Period-Luminosity Relation from Direct Distances to Cepheids in the LMC

We have applied the infrared surface brightness (ISB) technique to derive distances to 13 Cepheid variables in the LMC which have periods from 3-42 days. The corresponding absolute magnitudes define PL relations in VIWJK bands which agree exceedingly well with the corresponding Milky Way relations obtained from the same technique, and are in significant disagreement with the observed LMC Cepheid PL relations, by OGLE-II and Persson et al., in these bands. Our data uncover a systematic error in the p-factor law which transforms Cepheid radial velocities into pulsational velocities. We correct the p-factor law by requiring that all LMC Cepheids share the same distance. Re-calculating all Milky Way and LMC Cepheid distances with the revised p-factor law, we find that the PL relations from the ISB technique both in LMC and in the Milky Way agree with the OGLE-II and Persson et al. LMC PL relations, supporting the conclusion of no metallicity effect on the slope of the Cepheid PL relation in optical/near infrared bands.Comment: 4 pages, to appear in the proceedings of the "Stellar Pulsation and Evolution" conference, Monte Porzio Catone, June 200

Infrared Surface Brightness Distances to Cepheids: a comparison of Bayesian and linear-bisector calculations

We have compared the results of Bayesian statistical calculations and linear-bisector calculations for obtaining Cepheid distances and radii by the infrared surface brightness method. We analyzed a set of 38 Cepheids using a Bayesian Markov Chain Monte Carlo method that had been recently studied with a linear-bisector method. The distances obtained by the two techniques agree to 1.5 \pm 0.6% with the Bayesian distances being larger. The radii agree to 1.1% \pm 0.7% with the Bayesian determinations again being larger. We interpret this result as demonstrating that the two methods yield the same distances and radii. This implies that the short distance to the LMC found in recent linear-bisector studies of Cepheids is not caused by deficiencies in the mathematical treatment. However, the computed uncertainties in distance and radius for our dataset are larger in the Bayesian calculation by factors of 1.4-6.7. We give reasons to favor the Bayesian computations of the uncertainties. The larger uncertainties can have a significant impact upon interpretation of Cepheid distances and radii obtained from the infrared surface brightness method.Comment: 27 pages with 9 figure

An Atlas of H-alpha and R Images and Radial Profiles of 29 Bright Isolated Spiral Galaxies

Narrow-band H-alpha+[NII] and broadband R images and surface photometry are presented for a sample of 29 bright (M_B < -18) isolated S0-Scd galaxies within a distance of 48 Mpc. These galaxies are among the most isolated nearby spiral galaxies of their Hubble classifications as determined from the Nearby Galaxies Catalog (Tully 1987a).Comment: To appear in Astrophysical Journal Supplement Series. 17 pages, including 8 atlas pages in JPEG format. Version with high resolution figures available at http://www1.union.edu/~koopmanr/preprints.htm

Are the HI deficient galaxies on the outskirts of Virgo recent arrivals?

The presence on the Virgo cluster outskirts of spiral galaxies with gas deficiencies as strong as those of the inner galaxies stripped by the intracluster medium has led us to explore the possibility that some of these peripheral objects are not newcomers. A dynamical model for the collapse and rebound of spherical shells under the point mass and radial flow approximations has been developed to account for the amplitude of the motions in the Virgo I cluster (VIC) region. According to our analysis, it is not unfeasible that galaxies far from the cluster, including those in a gas-deficient group well to its background, went through its core a few Gyr ago. The implications would be: (1) that the majority of the HI-deficient spirals in the VIC region might have been deprived of their neutral hydrogen by interactions with the hot intracluster medium; and (2) that objects spending a long time outside the cluster cores might keep the gas deficient status without altering their morphology.Comment: Accepted for publication in ApJ. 4 pages, 3 figures. Uses emulateapj

Improving the mass determination of Galactic Cepheids

We have selected a sample of Galactic Cepheids for which accurate estimates of radii, distances, and photometric parameters are available. The comparison between their pulsation masses, based on new Period-Mass-Radius (PMR) relations, and their evolutionary masses, based on both optical and NIR Color-Magnitude (CM) diagrams, suggests that pulsation masses are on average of the order of 10% smaller than the evolutionary masses. Current pulsation masses show, at fixed radius, a strongly reduced dispersion when compared with values published in literature.The increased precision in the pulsation masses is due to the fact that our predicted PMR relations based on nonlinear, convective Cepheid models present smaller standard deviations than PMR relations based on linear models. At the same time, the empirical radii of our Cepheid sample are typically accurate at the 5% level. Our evolutionary mass determinations are based on stellar models constructed by neglecting the effect of mass-loss during the He burning phase. Therefore, the difference between pulsation and evolutionary masses could be intrinsic and does not necessarily imply a problem with either evolutionary and/or nonlinear pulsation models. The marginal evidence of a trend in the difference between evolutionary and pulsation masses when moving from short to long-period Cepheids is also briefly discussed. The main finding of our investigation is that the long-standing Cepheid mass discrepancy seems now resolved at the 10% level either if account for canonical or mild convective core overshooting evolutionary models.Comment: 14 pages, 4 postscript figures, accepted for publication on ApJ Letter

A Digital Archive of HI 21 cm Line Spectra of Optically-targeted Galaxies

We present a homogeneous compilation of HI spectral parameters extracted from global 21 cm line spectra for some 9000 galaxies in the local universe (heliocentric velocity -200 < V_Sun < 28,000 km/s) obtained with a variety of large single dish radio telescopes but reanalyzed using a single set of parameter extraction algorithms. Corrections to the observed HI line flux for source extent and pointing offsets and to the HI line widths for instrumental broadening and smoothing are applied according to model estimates to produce a homogenous catalog of derived properties with quantitative error estimates. Where the redshift is available from optical studies, we also provide flux measurements for an additional 156 galaxies classified as marginal HI detections and rms noise limits for 494 galaxies classified as nondetections. Given the diverse nature of the observing programs contributing to it, the characteristics of the combined dataset are heterogeneous, and as such, the compilation is neither integrated HI line flux nor peak flux limited. However, because of the large statistical base and homogenous reprocessing, the spectra and spectral parameters of galaxies in this optically targeted sample can be used to complement data obtained at other wavelengths to characterize the properties of galaxies in the local universe and to explore the large scale structures in which they reside.Comment: 13 pages, 9 figures, 3 external online tables, accepted for publication in ApJ