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Magnetars are young neutron stars with extreme magnetic fields (B [?] 1014-1015 G). How these fields relate to the properties of their progenitor stars is not yet clearly established. However, from the few objects associated with young clusters it has been possible to estimate the initial masses of the progenitors, with results indicating that a very massive progenitor star (M prog> 40 M $_{\normalsize \odot }$) is required to produce a magnetar. Here, we present adaptive-optics assisted Keck/NIRC2 imaging and Keck/NIRSPEC spectroscopy of the cluster associated with the magnetar SGR 1900+14, and report that the initial progenitor star mass of the magnetar was a factor of 2 lower than this limit, M prog = 17 +- 2 M $_{\normalsize \odot }$. Our result presents a strong challenge to the concept that magnetars can only result from very massive progenitors. Instead, we favor a mechanism which is dependent on more than just initial stellar mass for the production of these extreme magnetic fields, such as the "fossil-field" model or a process involving close binary evolution.

The quantitative spectral analysis of medium resolution optical spectra of A and B supergiants obtained with DEIMOS and ESI at the Keck Telescopes is used to determine a distance modulus of 24.93 +- 0.11 mag (968 +- 50 kpc) for the Triangulum Galaxy M33. The analysis yields stellar effective temperatures, gravities, interstellar reddening, and extinction, the combination of which provides a distance estimate via the flux-weighted gravity-luminosity relationship (FGLR). This result is based on an FGLR calibration that is continually being polished. An average reddening of [?]E(B - V)[?] [?] 0.08 mag is found, with a large variation ranging from 0.01 to 0.16 mag, however, demonstrating the importance of accurate individual reddening measurements for stellar distance indicators in galaxies with evident signatures of interstellar absorption. The large-distance modulus found is in good agreement with recent work on eclipsing binaries, planetary nebulae, long-period variables, RR Lyrae stars, and also with Hubble Space Telescope (HST) observations of Cepheids, if reasonable reddening assumptions are made for the Cepheids. Since distances based on the tip of the red giant branch (TRGB) method found in the literature give conflicting results, we have used HST Advanced Camera for Surveys V- and I-band images of outer regions of M33 to determine a TRGB distance of 24.84 +- 0.10 mag, in basic agreement with the FGLR result. We have also determined stellar metallicities and discussed the metallicity gradient in the disk of M33. We find metallicity of Z at the center and 0.3 Z in the outskirts at a distance of one isophotal radius. The average logarithmic metallicity gradient is -0.07 +- 0.01 dex kpc-1. However, there is a large scatter around this average value, very similar to what has been found for the H II regions in M33.

We have obtained deep near-infrared images in J and K filters of four fields in the Sculptor Group spiral galaxy NGC 247 with the ESO VLT and Infrared Spectrometer and Array Camera. For a sample of 10 Cepheids in these fields, previously discovered by Garcia-Varela et al. from optical wide-field images, we have determined mean J and K magnitudes and have constructed the period-luminosity (PL) relations in these bands. Using the near-infrared PL relations together with those in the optical V and I bands, we have determined a true distance modulus for NGC 247 of 27.64 mag, with a random uncertainty of +-2% and a systematic uncertainty of [?]4% which is dominated by the effect of unresolved stars on the Cepheid photometry. The mean reddening affecting the NGC 247 Cepheids of E(B - V) = 0.18 +- 0.02 mag is mostly produced in the host galaxy itself and is significantly higher than what was found in the previous optical Cepheid studies in NGC 247 of our own group, and Madore et al., leading to a 7% decrease in the previous optical Cepheid distance. As in other studies of our project, the distance modulus of NGC 247 we report is tied to an assumed Large Magellanic Cloud distance modulus of 18.50. Comparison with other distance measurements to NGC 247 shows that the present IR-based Cepheid distance is the most accurate among these determinations. With a distance of 3.4 Mpc, NGC 247 is about 1.5 Mpc more distant than NGC 55 and NGC 300, two other Sculptor Group spirals analyzed before with the same technique by our group.

We have obtained new spectrophotometric data for 28 H II regions in the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection of several auroral lines, including [O III] l4363, [S III] l6312, and [N II] l5755, has allowed us to measure electron temperatures and direct chemical abundances for the whole sample. We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines, and obtain the following least-square solution: 12 + log(O/H) = 8.57(+-0.02) - 0.41(+-0.03)R/R 25, where the galactocentric distance is expressed in terms of the isophotal radius R 25. The characteristic oxygen abundance, measured at 0.4 x R 25, is 12 + log(O/H) = 8.41. The gradient corresponds to -0.077 +- 0.006 dex kpc-1, and agrees very well with the galactocentric trend in metallicity obtained for 29 B and A supergiants in the same galaxy, -0.081 +- 0.011 dex kpc-1. The intercept of the regression for the nebular data virtually coincides with the intercept obtained from the stellar data, which is 8.59(+-0.05). This allows little room for depletion of nebular oxygen onto dust grains, although in this kind of comparison we are somewhat limited by systematic uncertainties, such as those related to the atomic parameters used to derive the chemical compositions. We discuss the implications of our result with regard to strong-line abundance indicators commonly used to estimate the chemical compositions of star-forming galaxies, such as R 23. By applying a few popular calibrations of these indices based on grids of photoionization models on the NGC 300 H II region fluxes, we find metallicities that are higher by 0.3 dex (a factor of 2) or more relative to our nebular (Te based) and stellar ones. We detect Wolf-Rayet stellar emission features in [?]1/3 of our H II region spectra, and find that in one of the nebulae hosting these hot stars the ionizing field has a particularly hard spectrum, as gauged by the "softness" parameter e = (O+/O++)/(S+/S++). We suggest that this is related to the presence of an early WN star. By considering a larger sample of extragalactic H II regions we confirm, using direct abundance measurements, previous findings of a metallicity dependence of e, in the sense that softer stellar continua are found at high metallicity.

We have analyzed the double-lined eclipsing binary system OGLE-051019.64-685812.3 in the LMC which consists of two G4 giant components with very similar effective temperatures. A detailed analysis of the Optical Gravitational Lensing Experiment I-band light curve of the system, radial velocity curves for both components derived from high-resolution spectra, and near-infrared magnitudes of the binary system measured outside the eclipses has allowed us to obtain an accurate orbit solution for this eclipsing binary and its fundamental physical parameters. Using a surface brightness (V - K)-color relation for giant stars we have calculated the distance to the system and obtained a true distance modulus of 18.50 mag, with an estimated total uncertainty of +-3%. More similar eclipsing binary systems in the LMC which we have discovered and for which we are currently obtaining the relevant data will allow us to better check on the systematics of the method and eventually provide a distance determination to the LMC accurate to 1%, much needed for the calibration of the distance scale.

The location of the Scutum Red Supergiant (RSG) clusters at the end of the Galactic Bar makes them an excellent probe of the Galaxy's secular evolution, while the clusters themselves are ideal testbeds in which to study the predictions of stellar evolutionary theory. To this end, we present a study of the RSG's surface abundances using a combination of high-resolution Keck/NIRSPEC H-band spectroscopy and spectral synthesis analysis. We provide abundance measurements for elements C, O, Si, Mg, Ti, and Fe. We find that the surface abundances of the stars studied are consistent with CNO burning and deep, rotationally enhanced mixing. The average a/Fe ratios of the clusters are solar, consistent with a thin-disk population. However, we find significantly subsolar Fe/H ratios for each cluster, a result which strongly contradicts a simple extrapolation of the Galactic metallicity gradient to lower Galactocentric distances. We suggest that a simple one-dimensional parameterization of the Galaxy's abundance patterns is insufficient at low Galactocentric distances, as large azimuthal variations may be present. Indeed, we show that the abundances of O, Si, and Mg are consistent with independent measurements of objects in similar locations in the Galaxy. In combining our results with other data in the literature, we present evidence for large-scale ([?] kpc) azimuthal variations in abundances at Galactocentric distances of 3-5 kpc. While we cannot rule out that this observed behavior is due to systematic offsets between different measurement techniques, we do find evidence for similar behavior in a study of the barred spiral galaxy NGC 4736 which uses homogeneous methodology. We suggest that these azimuthal abundance variations could result from the intense but patchy star formation driven by the potential of the central bar.

The Galactic center (GC) has experienced a high degree of recent star-forming activity, as evidenced by the large number of massive stars currently residing there. The relative abundances of chemical elements in the GC may provide insights into the origins of this activity. Here, we present high-resolution H-band spectra of two red supergiants (RSGs) in the GC (IRS 7 and VR 5-7), and in combination with spectral synthesis we derive abundances for Fe and C, as well as other a-elements Ca, Si, Mg Ti, and O. We find that the C depletion in VR 5-7 is consistent with the predictions of evolutionary models of RSGs, while the heavy depletion of C and O in IRS 7's atmosphere is indicative of deep mixing, possibly due to fast initial rotation and/or enhanced mass loss. Our results indicate that the current surface Fe/H content of each star is slightly above solar. However, comparisons to evolutionary models indicate that the initial Fe-to-H ratio was likely closer to solar, and has been driven higher by H depletion at the stars' surface. Overall, we find a-to-Fe ratios for both stars, which are consistent with the thin Galactic disk. These results are consistent with other chemical studies of the GC, given the precision to which abundances can currently be determined. We argue that the GC abundances are consistent with a scenario in which the recent star-forming activity in the GC was fueled by either material traveling down the Bar from the inner disk, or from the winds of stars in the inner bulge--with no need to invoke top-heavy stellar initial mass functions to explain anomalous abundance ratios.

In order to better determine the physical properties of hot, massive stars as a function of metallicity, we obtained very high signal-to-noise ratio optical spectra of 26 O and early B stars in the Magellanic Clouds. These allow accurate modeling even in cases where the He I l4471 line has an equivalent width of only a few tens of m A. The spectra were modeled with FASTWIND, with good fits obtained for 18 stars; the remainder show signatures of being binaries. We include stars in common to recent studies to investigate possible systematic differences. The "automatic" FASTWIND modeling method of Mokiem and collaborators produced temperatures 1100 K hotter on average, presumably due to the different emphasis given to various temperature-sensitive lines. More significant, however, is that the automatic method always produced a "best" result for each star, even ones we identify as composite (binaries). The temperatures found by the TLUSTY/CMFGEN modeling of Bouret, Heap, and collaborators yielded temperatures 1000 K cooler than ours, on average. Significant outliers were due either to real differences in the data (some of the Bouret/Heap data were contaminated by moonlight continua) or the fact that we could detect the He I line needed to better constrain the temperature. Our new data agree well with the effective temperature scale we previously presented. We confirm that the "Of" emission characteristics do not track luminosity classes in exactly the same manner as in Milky Way stars. We revisit the issue of the "mass discrepancy," finding that some of the stars in our sample do have spectroscopic masses that are significantly smaller than those derived from stellar evolutionary models. We do not find that the size of the mass discrepancy is simply related to either effective temperature or surface gravity.

The quantitative analysis of low-resolution spectra of A and B supergiants is used to determine a distance modulus of 24.99 +- 0.10 mag ( 995 +- 46 kpc) to the Local Group galaxy WLM. The analysis yields stellar effective temperatures and gravities, which provide a distance through the flux-weighted gravity-luminosity relationship (FGLR). Our distance is 0.07 mag larger than the most recent results based on Cepheids and the tip of the red giant branch. This difference is within the 1 s overlap of the typical uncertainties quoted in these photometric investigations. In addition, non-LTE spectral synthesis of the rich metal-line spectra (mostly iron, chromium, and titanium) of the A supergiants is carried out, which allows the determination of stellar metallicities. An average metallicity of - 0.87 +- 0.06 dex with respect to solar metallicity is found.

We have obtained deep images in the near-infrared J and K filters for several fields in the Local Group galaxy WLM. We report intensity mean magnitudes for 31 Cepheids located in these fields, which we previously discovered in a wide-field optical imaging survey of WLM. The data define tight period-luminosity relations in both near-infrared bands, which we use to derive the total reddening of the Cepheids in WLM and the true distance modulus of the galaxy from a multiwavelength analysis of the reddened distance moduli in the VIJK bands. From this, we obtain the values E(B [?] V) = 0.082 +- 0.02 and (m [?] M)0 = 24.924 +- 0.042 mag, with a systematic uncertainty in the distance of about +-3%. This Cepheid distance agrees extremely well with the distance of WLM determined from the I-band tip of the red giant branch (TRGB) method by ourselves and others. Most of the reddening of the Cepheids in WLM (0.06 mag) is produced inside the galaxy, demonstrating again the need for an accurate determination of the total reddening and/or the use of infrared photometry to derive Cepheid distances which are accurate to 3% or better, even for small irregular galaxies like WLM.

A quantitative spectral analysis of 24 A supergiants in the Sculptor Group spiral galaxy NGC 300 at a distance of 1.9 Mpc is presented. A new method is introduced to analyze low-resolution (~5 A) spectra, which yields metallicities accurate to 0.2 dex including the uncertainties arising from the errors in Teff (5%) and log g (0.2 dex). For the first time the stellar metallicity gradient based on elements such as titanium and iron in a galaxy beyond the Local Group is investigated. Solar metallicity is measured in the center and 0.3 solar in the outskirts and a logarithmic gradient of -0.08 dex kpc[?]1. An average reddening of E(B [?] V) [?] 0.12 mag is obtained, however, with a large variation from 0.07 to 0.24 mag. We also determine stellar radii, luminosities, and masses and discuss the evolutionary status. Finally, the observed relationship between absolute bolometric magnitudes Mbol and flux-weighted gravities gF = g/T4eff is investigated. At high temperatures the strength of the Balmer lines depends solely on the flux-weighted gravity, which allows a precise direct determination of log gF with an accuracy of 0.05-0.1 dex. We find a tight relationship between Mbol and log gF in agreement with stellar evolution theory. Combining these new results with previous work on Local Group galaxies, we obtain a new flux-weighted gravity-luminosity relationship (FGLR), which is very well defined and appears to be an excellent alternative tool to determine distances to galaxies.

We present new high-resolution near-IR spectroscopy and OH maser observations to investigate the population of cool luminous stars of the young massive Galactic cluster RSGC1. Using the 2.293 mm CO band-head feature, we make high-precision radial velocity measurements of 16 of the 17 candidate red supergiants (RSGs) identified by Figer et al. We show that F16 and F17 are foreground stars, while we confirm that the rest are indeed physically associated RSGs. We determine that star F15, also associated with the cluster, is a yellow hypergiant based on its luminosity and spectroscopic similarity to r Cas. Using the cluster's radial velocity, we have derived the kinematic distance to the cluster and revisited the stars' temperatures and luminosities. We find a larger spread of luminosities than in the discovery paper, consistent with a cluster age 30% older than previously thought ( 12 +- 2 Myr), and a total initial mass of (3 +- 1) x 104 M. The spatial coincidence of the OH maser with F13, combined with similar radial velocities, is compelling evidence that the two are related. Combining our results with recent SiO and H2O maser observations, we find that those stars with maser emission are the most luminous in the cluster. From this we suggest that the maser active phase is associated with the end of the RSG stage, when the luminosity-mass ratios are at their highest.

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 Pietrzynski 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. 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 +- 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 +- 0.037 mag (random error), corresponding to a distance of 1.94 +- 0.03 Mpc. This value is tied to an adopted true Large Magellanic Cloud (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 +-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.

We present multiobject spectroscopy of young, massive stars in the Local Group galaxy IC 1613. We provide the spectral classification and a detailed spectral catalog for 54 OBA stars in this galaxy. The majority of the photometrically selected sample is composed of B- and A-type supergiants. The remaining stars include early O-type dwarfs and the only Wolf-Rayet star known in this galaxy. Among the early B stars we have serendipitously uncovered six Be stars, the largest spectroscopically confirmed sample of this class of objects beyond the Magellanic Clouds. We measure chemical abundances for nine early B supergiants, and find a mean oxygen abundance of 12 + log (O/H) = 7.90 +- 0.08. This value is consistent with the result we obtain for two H II regions in which we detect the temperature-sensitive [O III] l4363 auroral line.

We report on the unprecedented red supergiant (RSG) population of a massive young cluster, located at the base of the Scutum-Crux Galactic arm. We identify candidate cluster RSGs based on 2MASS photometry and medium-resolution spectroscopy. With follow-up high-resolution spectroscopy, we use CO band-head equivalent width and high-precision radial velocity measurements to identify a core grouping of 26 physically associated RSGs--the largest such cluster known to date. Using the stars' velocity dispersion and their inferred luminosities in conjunction with evolutionary models, we argue that the cluster has an initial mass of ~40,000 M and is therefore among the most massive in the galaxy. Further, the cluster is only a few hundred parsecs away from the cluster of 14 RSGs recently reported by Figer at al.. These two RSG clusters represent 20% of all known RSGs in the Galaxy, and now offer the unique opportunity to study the presupernova evolution of massive stars, and the blue- to red-supergiant ratio at uniform metallicity. We use GLIMPSE, MIPSGAL, and MAGPIS survey data to identify several objects in the field of the larger cluster which seem to be indicative of recent regionwide starburst activity at the point where the Scutum-Crux arm intercepts the Galactic bulge. Future abundance studies of these clusters will therefore permit the study of the chemical evolution and metallicity gradient of the Galaxy in the region where the disk meets the bulge.

As part of the Araucaria Project, we present the first spectral catalog of supergiant stars in the Local Group dwarf irregular galaxy WLM. In assigning a spectral classification to these stars we accounted for the low metal content of WLM relative to the galactic standards used in the MK process, by using classification criteria developed for B and A supergiants contained in the Small Magellanic Cloud. Our spectral catalog shows that our higher signal-to-noise ratio (S/N) spectroscopic sample of 19 objects contains at least six early B (B0-B5) supergiants and six late B and early A (B8-A2) stars of luminosity class between Ia and II, as well as an O7 V star and an O9.7 Ia star. The spectra of several of these stars are of sufficiently high quality for a determination of the stellar parameters and abundances. We have also acquired a second set of lower S/N spectra for mostly BA stars; however, their quality does not allow a further analysis. We have carried out a quantitative analysis for three early B supergiants. The mean oxygen abundance we derive is 12 + log(O/H) = 7.83 +- 0.12. This value agrees very well with the measurement that is obtained from H II regions. We therefore find no additional evidence for the discrepancy between stellar and nebular oxygen abundances measured for a single A-type supergiant by Venn et al. The analysis of B- and A-type supergiants yields compatible results for nitrogen, silicon, and magnesium. We show that the photometric variability of the blue supergiants included in our spectroscopic sample is negligible for the use of these stars as distance indicators.

We have obtained mosaic images of NGC 3109 in the V and I bands on 74 nights, spanning approximately 1 yr. 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 31.4 days. 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 construct period-luminosity relations from our data and obtain reddening-corrected distance moduli of 25.72 +- 0.03 mag in V and 25.66 +- 0.03 mag in I. The distance modulus derived from the reddening-independent V-I Wesenheit index turns out to be significantly shorter (25.54 +- 0.03 mag), which indicates that in addition to the foreground extinction of E(B-V) = 0.05 mag, there is an intrinsic to NGC 3109 reddening of about 0.05 mag. Our distance obtained based on the reddening-free Wesenheit magnitudes is consistent with earlier distance determinations of NGC 3109 from Cepheids and the tip of the red giant branch. We improve on our distance and extinction determination combining our optical data with the follow-up near-infrared observations of a subsample of NGC 3109 Cepheids.

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 and coworkers, accurate mean magnitudes were obtained from these data, which allowed us to determine with unprecedented accuracy the distance to NGC 6822 from a multiwavelength 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 ~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 by McGonegal and coworkers 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 & 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.

We have measured accurate near-infrared magnitudes in the J and K bands of 39 Cepheid variables in the irregular Local Group galaxy IC 1613 with well-determined periods and optical VI light curves. Using the template light curve approach of Soszynski, Gieren, & Pietrzynski, accurate mean magnitudes were obtained from these data, which allowed us to determine the distance to IC 1613 relative to the LMC from a multiwavelength period-luminosity solution in the optical VI and near-IR JK bands with an unprecedented accuracy. Our result for the IC 1613 distance is (m - M)0 = 24.291 +- 0.035 (random error) mag, with an additional systematic uncertainty smaller than 2%. From our multiwavelength approach, we find for the total (average) reddening to the IC 1613 Cepheids E(B - V) = 0.090 +- 0.019 mag, which is significantly higher than the foreground reddening of about 0.03 mag, showing the presence of appreciable dust extinction inside the galaxy. Our data suggest that the extinction law in IC 1613 is very similar to the Galactic one. Our distance result agrees, within the uncertainties, with two earlier infrared Cepheid studies in this galaxy, of Macri et al. (from HST data on 4 Cepheids) and McAlary et al. (from ground-based H-band photometry of 10 Cepheids), but our result has reduced the total uncertainty on the distance to IC 1613 (relative to the LMC) to less than 3%. With distances to nearby galaxies from Cepheid infrared photometry at this level of accuracy, which are currently being obtained in our Araucaria Project, it seems possible to significantly reduce the systematic uncertainty of the Hubble constant, as derived from the HST Key Project approach, by improving the calibration of the metallicity effect on PL relation zero points and by improving the distance determination to the LMC.

We have used the Advanced Camera for Surveys on board the Hubble Space Telescope to obtain deep photometry of the NGC 300 spiral galaxy in the Sculptor group. The results have been used to derive an accurate distance determination based on the tip of the red giant branch distance estimator. Both edge-detection and maximum likelihood methods have been applied to derive a distance modulus (m - M)0 = 26.30 +- 0.03 +- 0.12 for edge detection and (m - M)0 = 26.36 +- 0.02 +- 0.12 for maximum likelihood. These results are fully consistent with the recent distance estimate derived from near-IR photometry of Cepheids variable stars in the context of the Araucaria project, (m - M)0 = 26.37 +- 0.05 +- 0.03 (Gieren and coworkers).

We have used the Advanced Camera for Surveys aboard the Hubble Space Telescope (HST) 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 WI are not significantly different from the relations obtained without corrections. We fix an upper limit of 0.04 mag 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.

We have obtained deep near-infrared images in J and K filters of three fields in the Sculptor galaxy NGC 300 with the ESO VLT and ISAAC Camera. For 16 Cepheid variables in these fields, we have determined J and K magnitudes at two different epochs and have derived their mean magnitudes in these bands. The slopes of the resulting period-luminosity relations are in very good agreement with the slopes of these relations measured in the Large Magellanic Cloud (LMC) by Persson et al. Fitting the LMC slopes to our data, we have derived distance moduli in J and K. Using these values together with the values derived in the optical V and I bands in our previous work, we have determined an improved total reddening for NGC 300 of E(B - V) = 0.096 +- 0.006 mag, which yields extremely consistent values for the absorption-corrected distance modulus of the galaxy from VIJK bands. Our distance result for NGC 300 from this combined optical/near-infrared Cepheid study is (m - M)0 = 26.37 +- 0.05 (random) +- 0.03 (systematic) mag and is tied to an adopted true LMC distance modulus of 18.50 mag. Both random and systematic uncertainties are dominated by photometric errors, while errors due to reddening, metallicity effects, and crowding are less important. Our distance determination is consistent with the earlier result from near-infrared (H-band) photometry of two Cepheids in NGC 300 by Madore et al., but far more accurate. Our distance value also agrees with the HST Key Project result of Freedman et al. and with the recent distance estimate for NGC 300 from Butler et al. from the tip of the red giant branch (TRGB) I-band magnitude when our improved reddening is used to calculate the absorption corrections. Our distance results from the different optical and near-infrared bands indicate that the reddening law in NGC 300 must be very similar to the Galactic one. With the results of this work, the distance of NGC 300 relative to the LMC now seems determined with an accuracy of approximately +-3%. The distance to this nearby Sculptor galaxy is therefore now known with higher accuracy than that of most (nearer) Local Group galaxies.

The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution and yet is difficult to measure with current techniques. In this paper we investigate new metallicity indicators based on the strengths of stellar photospheric features at rest-frame ultraviolet wavelengths. By combining the evolutionary spectral synthesis code Starburst99 with the output from the non-LTE model atmosphere code WM-basic, we have developed a code that can model the integrated ultraviolet stellar spectra of star-forming regions at metallicities between 1/20 and twice solar. We use our models to explore a number of spectral regions that are sensitive to metallicity and clean of other spectral features. The most promising metallicity indicator is an absorption feature between 1935 and 2020 A, which arises from the blending of numerous Fe III transitions. We compare our model spectra with observations of two well-studied high-redshift star-forming galaxies, MS 1512-cB58 (a Lyman break galaxy at zem = 2.7276) and Q1307-BM1163 (a UV-bright galaxy at zem = 1.411). The profiles of the photospheric absorption features observed in these galaxies are well reproduced by the models. In addition, the metallicities inferred from their equivalent widths are in good agreement with previous determinations based on interstellar absorption and nebular emission lines. Our new technique appears to be a promising alternative, or complement, to established methods, which have only a limited applicability at high redshifts.

We present a study of the photometric variability of spectroscopically confirmed supergiants in NGC 300, comprising 28 epochs extending over a period of 5 months. We find 15 clearly photometrically variable blue supergiants in a sample of nearly 70 such stars, showing maximum light amplitudes ranging from 0.08 to 0.23 mag in the V band, and one variable red supergiant. We show their light curves and determine semiperiods for two A2 Ia stars. Assuming that the observed changes correspond to similar variations in bolometric luminosity, we test for the influence of this variability on the flux-weighted gravity-luminosity relationship and find a negligible effect, showing that the calibration of this relationship, which has the potential to measure extragalactic distances at the Cepheid accuracy level, is not affected by stellar photometric variability in any significant way.

We analyze Space Telescope Imaging Spectrograph (STIS) spectra in the 1150-1700 A wavelength range obtained for six early B supergiants in the neighboring galaxy M31. Because of their likely high (nearly solar) abundance, these stars were originally chosen to be directly comparable to their Galactic counterparts and represent a much needed addition to our current sample of B-type supergiants, in our efforts to study the dependence of the wind momentum-luminosity relationship on spectral type and metallicity. As a first step to determine wind momenta we fit the P Cygni profiles of the resonance lines of N V, Si IV, and C IV with standard methods and derive terminal velocities for all of the STIS targets. From these lines we also derive ionic stellar wind column densities. Our results are compared with those obtained previously in Galactic supergiants and confirm earlier claims of "normal" wind line intensities and terminal velocities in M31. For one-half of the sample we find evidence for an enhanced maximum turbulent velocity when compared to Galactic counterparts.

We have obtained VLT low-resolution (~5 A) multiobject spectroscopy in the 4000-5000 A spectral range of about 70 blue supergiant candidates in the Sculptor Group spiral galaxy NGC 300, selected from previous wide-field photometry. Of the 62 spectroscopically confirmed blue supergiants, with spectral types ranging from late O to F, 57 have types between early B and mid-A. We present a detailed spectral catalog containing identification, magnitudes, colors, and spectral types. We employ synthetic spectra calculated from blue supergiant model atmospheres for different metallicities to determine metal abundances for two A0 supergiants of the sample. In agreement with the expectations, the star closer to the galactic center is found to be more metal-rich than the object at a larger galactocentric distance. We will employ this technique on the whole supergiant sample to determine the stellar abundance gradient in the disk of NGC 300, together with the internal reddening from a comparison of the observed versus synthetic colors. This will allow, among other things, an accurate calibration of the effect of metallicity on the Cepheid period-luminosity relation. Using the Balmer Hb line profile, we have estimated the mass-loss rate for one of the brightest A2 supergiants in the sample. Under additional reasonable assumptions, we determined the wind momentum of the star and compared it with the value expected from the empirical wind momentum-luminosity relationship (WLR) for A-type supergiants of Kudritzki et al. Good agreement is obtained. We will derive mass-loss rates and wind momenta for all stars in our sample from the Ha line profiles in forthcoming work, and we will then thoroughly test the usefulness of the WLR for distance measurement out to about 15 Mpc.

High-quality Keck HIRES echelle spectra of two A-supergiants in M31, designated 41-3654 (spectral type A2 Ia-O) and 41-3712 (A3 Ia-O), at 10.2 kpc galactocentric distance are analyzed by means of NLTE unified model atmospheres to determine the properties of their stellar winds, in particular the wind momenta. We obtain mass-loss rates of 1.9 x 10-6 and 1.1 x 10-6 M yr-1 for 41-3654 and 41-3712, respectively, with an accuracy of 15% from the fit of the Ha profiles. The terminal velocities are 200 +- 25 km s-1. In addition, the exponents of the wind velocity fields are determined (b = 2 and 3, respectively) and microturbulent velocities of the order of 20 km s-1 are found. The wind momenta of the two targets are in excellent agreement with the wind momentum-luminosity relation (WLR) for galactic A- and B-supergiants. We discuss the potential of the WLR for extragalactic distance determinations and conclude that it may allow independent distance moduli to be obtained with an accuracy of 10%.