Sigma One

We demonstrate that it is possible to calculate not only the mean of an underlying population but also its dispersion, given only a single observation and physically reasonable constraints (i.e., that the quantities under consideration are non-negative and bounded). We suggest that this counter-intuitive conclusion is in fact at the heart of most modeling of astronomical data.Comment: Accepted to the Astronomical Journal. 13 pages, 4 figure

The Feinheit method: A phase-independent formulation of the period-luminosity relation for Cephids

The tight correlation between color and luminosity during the cyclical variation of a Cepheid is calibrated and shown to be a direct means by which most of the phase-dependent temperature-induced amplitude of the variable can be transformed away. The resulting Feinheit function, F = V - alpha (B-V) gives rise to a random-phase period-luminosity relation with an rms scatter of less than 0.20 mag. A comparison shows that the blue Feinheit method for distance determinations method from single-phase observations is as accurate as near-infrared photometry but has the added advantage of being able to use panoramic detectors for the data acquisition. The Feinheit function is identified as the surface area variation of the Cepheid during its cycle

Two New Tests of the Metallicity Sensitivity of the Cepheid Period-Luminosity Relation (The Leavitt Law)

We undertake a new test of the metallicity sensitivity of the Leavitt Law for Classical Cepheids. We derive an empirical calibration of the apparent luminosities of Cepheids as measured from the optical through the mid-infrared (0.45-8.0um) as a function of spectroscopic [Fe/H] abundances of individual Cepheids in the Large Magellanic Cloud from Romaniello et al. (2008). The cumulative trend over the entire wavelength range shows a nearly monotonic behavior. The sense of the trend is consistent with differential line-blanketing in the optical, leading to stars of high metallicity being fainter in the optical. This is followed by a reversal in the trend at longer wavelengths, with the cross-over occurring near the K band at about 2.2um, consistent with a subsequent redistribution of energy resulting in a mild brightening of Cepheids (with increased metallicity) at mid-infrared wavelengths. This conclusion agrees with that of Romaniello et al. based on a differential comparison of the mean V- and K-band Leavitt Laws for the Galaxy, SMC and LMC, but is opposite in sign to most other empirical tests of the sensitivity of Cepheid distances to mean [O/H] HII region abundances. We also search for a correlation of Cepheid host-galaxy metallicity with deviations of the galaxy's Cepheid distance from that predicted from a pure Hubble flow. Based on Cepheid distances to 26 nearby galaxies in the local flow, only a very weak signal is detected giving Dmu_o = -0.17 (+/- 0.31) ([O/H] - 8.80) - 0.21 (+/-0.10). This is in agreement with previous determinations, but statistically inconclusive.Comment: Accepted to the Astrophysical Journal. 8 pages, 5 figures, 1 tabl

Cepheid and Tip of the Red Giant Branch Distances To the Dwarf Irregular Galaxy IC10

We present color-magnitude diagrams and luminosity functions of stars in the nearby galaxy IC 10, based on VI CCD photometry acquired with the COSMIC prime-focus camera on the Palomar 5m telescope. The apparent I-band luminosity function of stars in the halo of IC 10 shows an identifiable rise at I~21.7 mag. This is interpreted as being the tip of the red giant branch (TRGB) at M_V~-4 mag. Since IC 10 is at a very low Galactic latitude, its foreground extinction is expected to be high and the uncertainty associated with that correction is the largest contributor to the error associated with its distance determination. Multi-wavelength observations of Cepheid variable stars in IC 10 give a Population I distance modulus of 24.1 +- 0.2 mag, which corresponds to a linear distance of 660 +- 66 kpc for a total line-of-sight reddening of E(B-V) = 1.16 +- 0.08 mag, derived self-consistently from the Cepheid data alone. Applying this Population I reddening to the Population II halo stars gives a TRGB distance modulus of 23.5 +- 0.2 mag, corresponding to 500 +- 50 kpc. We consider this to be a lower limit on the TRGB distance. Reconciling the Cepheid and TRGB distances would require that the reddening to the halo is $\Delta$E(B-V) = 0.31 mag lower than that into the main body of the galaxy. This then suggests that the Galactic extinction in the direction of IC10 is (B-V) ~ 0.85

Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies: II. Surface Photometry and the Properties of the Underlying Stellar Population

We present the results from an analysis of surface photometry of B, R, and Halpha images of a total of 114 nearby galaxies drawn from the Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf galaxies. Surface brightness and color profiles for the complete sample have been obtained. We determine the exponential and Sersic profiles that best fit the surface brightness distribution of the underlying stellar population detected in these galaxies. We also compute the (B-R) color and total absolute magnitude of the underlying stellar population and compared them to the integrated properties of the galaxies in the sample. Our analysis shows that the (B-R) color of the underlying population is systematically redder than the integrated color, except in those galaxies where the integrated colors are strongly contaminated by line and nebular-continuum emission. We also find that galaxies with relatively red underlying stellar populations (typically (B-R)>~1mag) show structural properties compatible with those of dwarf elliptical galaxies (i.e. a smooth light distribution, fainter extrapolated central surface brightness and larger scale lengths than BCD galaxies with blue underlying stellar populations). At least ~15% of the galaxies in the sample are compatible with being dwarf elliptical (dE) galaxies experiencing a burst of star formation. For the remaining BCD galaxies in the sample we do not find any correlation between the recent star formation activity and their structural differences with respect to other types of dwarf galaxies.Comment: 35 pages, 6 figures, accepted for publication in ApJS. Postscript files of panels f1a-f1o of figure 1 are available online at http://www.ociw.edu/~agpaz/astro-ph/apjs2004

Fuzzy Surfaces of Genus Zero

A fuzzy version of the ordinary round 2-sphere has been constructed with an invariant curvature. We here consider linear connections on arbitrary fuzzy surfaces of genus zero. We shall find as before that they are more or less rigidly dependent on the differential calculus used but that a large number of the latter can be constructed which are not covariant under the action of the rotation group. For technical reasons we have been forced to limit our considerations to fuzzy surfaces which are small perturbations of the fuzzy sphere.Comment: 11 pages, Late

High Resolution Rotation Curves of Low Surface Brightness Galaxies

High resolution Halpha rotation curves are presented for five low surface brightness galaxies. These Halpha rotation curves have shapes different from those previously derived from HI observations, probably because of the higher spatial resolution of the Halpha observations. The Halpha rotation curves rise more steeply in the inner parts than the HI rotation curves and reach a flat part beyond about two disk scale lengths. With radii expressed in optical disk scale lengths, the rotation curves of the low surface brightness galaxies presented here and those of HSB galaxies have almost identical shapes. Mass modeling shows that the contribution of the stellar component to the rotation curves may be scaled to explain most of the inner parts of the rotation curves, albeit with high stellar mass-to-light ratios. On the other hand, well fitting mass models can also be obtained with lower contributions of the stellar disk. These observations suggest that the luminous mass density and the total mass density are coupled in the inner parts of these galaxies.Comment: Accepted for publication in ApJ Letter