The Araucaria Project: The effect of blending on the Cepheid distance to NGC 300 from Advanced Camera for Surveys images

We have used the Advanced Camera for Surveys aboard the Hubble Space Telescope to obtain F435W, F555W and F814W single-epoch images of six fields in the spiral galaxy NGC 300. Taking advantage of the superb spatial resolution of these images, we have tested the effect that blending of the Cepheid variables studied from the ground with close stellar neighbors, unresolved on the ground-based images, has on the distance determination to NGC 300. Out of the 16 Cepheids included in this study, only three are significantly affected by nearby stellar objects. After correcting the ground-based magnitudes for the contribution by these projected companions to the observed flux, we find that the corresponding Period-Luminosity relations in V, I and the Wesenheit magnitude W_I are not significantly different from the relations obtained without corrections. We fix an upper limit of 0.04 magnitudes to the systematic effect of blending on the distance modulus to NGC 300. As part of our HST imaging program, we present improved photometry for 40 blue supergiants in NGC 300.Comment: To be published in the Astrophysical Journa

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

Distributed Random Process for a Large-Scale Peer-to-Peer Lottery

Most online lotteries today fail to ensure the verifiability of the random process and rely on a trusted third party. This issue has received little attention since the emergence of distributed protocols like Bitcoin that demonstrated the potential of protocols with no trusted third party. We argue that the security requirements of online lotteries are similar to those of online voting, and propose a novel distributed online lottery protocol that applies techniques developed for voting applications to an existing lottery protocol. As a result, the protocol is scalable, provides efficient verification of the random process and does not rely on a trusted third party nor on assumptions of bounded computational resources. An early prototype confirms the feasibility of our approach

A Direct Distance to the LMC Cepheid HV 12198 from the Infrared Surface Brightness Technique

We report on a first application of the infrared surface brightness technique on a Cepheid in the Large Magellanic Cloud, the variable HV 12198 in the young globular cluster NGC 1866. From this one star, we determine a distance modulus of 18.42 +- 0.10 (random and systematic uncertainty) to the cluster. When the results on further member Cepheids in NGC 1866 become available, we expect to derive the distance to the LMC with a +- 3-4 percent accuracy, including systematic errors, from this technique.Comment: 4 pages, 4 figures, accepted in ApJ Letter

The Star Blended with the MOA-2008-BLG-310 Source Is Not the Exoplanet Host Star

High resolution Hubble Space Telescope (HST) image analysis of the MOA-2008-BLG-310 microlens system indicates that the excess flux at the location of the source found in the discovery paper cannot primarily be due to the lens star because it does not match the lens-source relative proper motion, $\mu_{\rm rel}$, predicted by the microlens models. This excess flux is most likely to be due to an unrelated star that happens to be located in close proximity to the source star. Two epochs of HST observations indicate proper motion for this blend star that is typical of a random bulge star, but is not consistent with a companion to the source or lens stars if the flux is dominated by only one star, aside from the lens. We consider models in which the excess flux is due to a combination of an unrelated star and the lens star, and this yields 95\% confidence level upper limit on the lens star brightness of $I_L > 22.44$ and $V_L >23.62$. A Bayesian analysis using a standard Galactic model and these magnitude limits yields a host star mass $M_h = 0.21 ^{+0.21}_{-0.09}~ M_\odot$, a planet mass of $m_p = 23.4 ^{+23.9}_{-9.9}~M_\oplus$ at a projected separation of $a_\perp = 1.12^{+0.16}_{-0.17},$AU. This result illustrates excess flux in a high resolution image of a microlens-source system need not be due to the lens. It is important to check that the lens-source relative proper motion is consistent with the microlensing prediction. The high resolution image analysis techniques developed in this paper can be used to verify the WFIRST exoplanet microlensing survey mass measurements.Comment: Submitted to AJ on March 18, 201

Cepheid variables in the LMC cluster NGC 1866. I. New BVRI CCD photometry

We report BV(RI)c CCD photometric data for a group of seven Cepheid variables in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The photometry was obtained as part of a program to determine accurate distances to these Cepheids by means of the infrared surface brightness technique, and to improve the LMC Cepheid database for constructing Cepheid PL and PLC relations. Using the new data together with data from the literature, we have determined improved periods for all variables. For five fundamental mode pulsators, the light curves are now of excellent quality and will lead to accurate distance and radius determinations once complete infrared light curves and radial velocity curves for these variables become available.Comment: To appear in ApJ Supp., AASTeX, 24 pages, 8 tables, 8 figure

Interstellar extinction towards the inner Galactic Bulge

DENIS observations in the J (1.2 micron) and K_S (2.15 micron) bands together with isochrones calculated for the RGB and AGB phase are used to draw an extinction map of the inner Galactic Bulge. The uncertainty in this method is mainly limited by the optical depth of the Bulge itself. A comparison with fields of known extinction shows a very good agreement. We present an extinction map for the inner Galactic Bulge (approx. 20 sq. deg.)Comment: 4 pages, 4 figures, accepted for publication in A&A as a letter, see also http://www-denis.iap.fr/articles/extinction

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

The Araucaria Project. An Accurate Distance to the Local Group Galaxy NGC 6822 from Near-Infrared Photometry of Cepheid Variables

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 Soszynski, Gieren and Pietrzynski, 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. From our data, we obtain a distance to NGC 6822 of (m-M)_{0} = 23.312 +- 0.021 (random error) mag, with an additional systematic uncertainty of about 3 %. This distance value is tied to an assumed LMC distance modulus of 18.50. From our multiwavelength approach, we find for the total (average) reddening to the NGC 6822 Cepheids E(B-V) = 0.356 +- 0.013 mag, which is in excellent agreement with a previous determination of McGonegal et al. from near-infrared photometry and implies significant internal reddening of the Cepheids in NGC 6822. Our present, definitive distance determination of NGC 6822 from Cepheids agrees within 2 % with the previous distance we had derived from optical photometry alone, but has significantly reduced error bars. Our Cepheid distance to NGC 6822 is in excellent agreement with the recent independent determination of Cioni and Habing from the I-band magnitude of the tip of the red giant branch. It also agrees well, within the errors, with the early determination of McGonegal et al. (1983) from random-phase H-band photometry of nine Cepheids.Comment: Accepted to be published in the Ap

The Araucaria Project. Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 55

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 Pietrzy{\'n}ski et al., we have determined mean J and K magnitudes from observations at two epochs, and derived distance moduli from the observed PL relations in these bands. Using these values together with the previously measured distance moduli in the optical V and I bands, we have determined a total mean reddening of the NGC 55 Cepheids of E(B-V)=0.127 $\pm$ 0.019 mag, which is mostly produced inside NGC 55 itself. For the true distance modulus of the galaxy, our multiwavelength analysis yields a value of 26.434 $\pm$ 0.037 mag (random error), corresponding to a distance of 1.94 $\pm$ 0.03 Mpc. This value is tied to an adopted true LMC distance modulus of 18.50 mag. The systematic uncertainty of our derived Cepheid distance to NGC 55 (apart from the uncertainty on the adopted LMC distance) is $\pm$4%, with the main contribution likely to come from the effect of blending of some of the Cepheids with unresolved companion stars. The distance of NGC 55 derived from our multiwavelength Cepheid analysis agrees within the errors with the distance of NGC 300, strengthening the case for a physical association of these two Sculptor Group galaxies.Comment: latex. ApJ accepte