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Madore, Barry F.

Publications and source records attributed to Madore, Barry F..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The Hubble Space Telescope extragalactic distance scale key project. 2: Photometry of WFC images of M81

The Extragalactic Distance Scale (H(sub o)) Key Project for Hubble Space Telescope (HST) aims to employ the Cepheid period-luminosity (P-L) relation to measure galaxy distances out as far as the Virgo Cluster. The vital steps in this program are (1) to obtain precise photometry of stellar images from the Wide Field Camera (WFC) exposures of selected galaxies, and (2) to calibrate this photometry to obtain reliable distances to these galaxies from the Cepheid P-L relation. We have used the DAOPHOT II and ALLFRAME programs to determine 28 instrumental magnitudes -- 22 of F555W (of about V) and six of F785LP (of about I) -- of all stars brighter than V of about 25 in each of two 2.56 arcmin x 2.56 arcmin WFC fields of M81. The reductions use a varying point-spread function to account for the field effects in the WFC optics and yield instrumental magnitudes with single epoch precision ranging from 0.09 to 0.24 mag, at V of about 21.8 to 23.8 -- the magnitude range of the 30 Cepheids that we have now identified in M81. For brighter stars (V of about 22), single epoch magnitudes are precise to 0.09 mag. The photometric calibration onto the Johnson V and Kron-Cousins I systems was determined from independent ground-based CCD observing at the Canada-France-Hawaii Telescope (CFHT) 3.6 m (confirmed by the Kitt Peak National Observatory (KPNO) 4.0 m) and from the Palomar 5.0 m (using the wide-field COSMIC camera) and 1.5 m telescopes. Secondary standards, taken from the COSMIC and CFHT frames, were established in each of the WFC fields in V and I, allowing a direct transformation from ALLFRAME magnitudes to calibrated V and I magnitudes, giving mean V of about 23 magnitudes accurate to of about +/- 0.1 mag. The stellar populations in M81 have been analyzed in terms of the luminosity functions and color magnitude diagrams (CMD) derived from these data, from which we identify numerous supergiants, and a CMD morphology similar to M33.

Hughes, Shaun M. G.↗
NASA NTRS1994

The Hubble Space Telescope Extragalactic Distance Scale Key Project. 1: The discovery of Cepheids and a new distance to M81

We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I magnitude system using a ground-based calibration. Apparent period-luminosity relations at V and I were constructed, from which apparent distance moduli were measured with respect to assumed values of mu(sub 0) = 18.50 mag and E(B - V) = 0.10 mag for the Large Magellanic Cloud. The difference in the apparent V and I moduli yields a measure of the difference in the total mean extinction between the M81 and the LMC Cepheid samples. A low total mean extinction to the M81 sample of E(B - V) = 0.03 +/- 0.05 mag is obtained. The true distance modulus to M81 is determined to be 27.80 +/- 0.20 mag, corresponding to a distance of 3.63 +/- 0.34 Mpc. These data illustrate that with an optimal (power-law) sampling strategy, the HST provides a powerful tool for the discovery of extragalactic Cepheids and their application to the distance scale. M81 is the first calibrating galaxy in the target sample of the HST Key Project on the Extragalactic Distance Scale, the ultimate aim of which is to provide a value of the Hubble constant to 10% accuracy.

Freedman, Wendy L.↗
NASA NTRS1994

The initial mass function for massive stars in the Magellanic Clouds. 1: UBV photometry and color-magnitude diagrams for 14 OB associations

UBV charge coupled device (CCD) photometry has been obtained for 14 OB associations in the Magellanic Clouds using the University of Toronto's 0.6 m telescope and the Carnegie Institution of Washington's 1.0 m reflector, both on Las Campanas, Chile. The data are presented and used to construct color-magnitude diagrams for the purposes of investigating the massive-star content of the associations.

Hill, Robert J.↗
NASA NTRS1993

Resolved stars in nearby galaxies: Ground-based photometry of M81

Using the Canada-France-Hawaii Telescope (CFHT) we have obtained three closely spaced epochs of calibrated Blue Violet Red Infrared (BVRI) CCD imaging of two fields in M81, each known to contain a thirty-day Cepheid. Calibrated BVRI photometry of the brightest stars in these fields is presented. The slope of the luminosity function from the brightest 3-4 mag of the main-sequence blue plume is consistent with similar determinations of the apparent luminosity function in other resolved galaxies, thereby removing the one potential deviation from universality noted by Freedman in a photographic study of luminosity functions in nearby resolved galaxies. Under the assumption that the two Cepheids are representative, a reddening-law fit to the multiwavelength BVRI period-luminosity moduli give a true distance modulus of (m-M)sub 0 = 27.79 mag for M81, corresponding to a linear distance of 3.6 Mpc. An error analysis shows that the derived true distance modulus has a random error of +/- 0.28 mag (due to the photometric uncertainties in the BVRI data), with a systematic uncertainty of +/- 0.10 mag (accounting for the combined effects of unknown phasing of the data points, and the unknown positioning of these particular stars within the Cepheid instabiliy strip).

Madore, Barry F.↗
NASA NTRS1993

A catalog of blue and red supergiants in M33

We present a catalog of blue and red stars in M33 based on photographic photometry of over 65,000 objects extracted from plates taken with the 3.6 m Canada-France-Hawaii Telescope (CFHT) and the 2.0 m Rozhen (Bulgarian) Telescope. The completeness limit of the various surveys are estimated here to be V = 19.5 mag for those stars situated in crowded associations, and V = 20.0 mag for stars in the interarm fields. We list magnitudes and positions for 2112 blue stars, defined by (U - V) less than 0.0 mag, (U - B) less than 0.0 mag, and V less than 19.5 mag, and 389 red stars defined by (B - V) greater than 1.8 mag and V less than 19.5 mag. Of these, 1156 are candidate O stars on the basis of (U - V) less than -0.9 mag.

Ivanov, Georgi R.↗
NASA NTRS1993

Stellar populations in the dwarf elliptical galaxy NGC 185

The study presents BVRI CCD photometry of about 5300 stars in the central area of the dwarf elliptical galaxy NGC 185 in the Local Group. The color-magnitude diagram shows three distinct stellar populations: a dominant RGB population, AGB stars located above the tip of the RGB stars, and a small number of young stars having blue to yellow colors. The foreground reddening is estimated to be 0.19 +/- 0.03 mag using the (B - V) - (V - I) diagram for the bright foreground stars with good photometry. Surface photometry of the central area of NGC 185 is presented; it shows that the colors become rapidly bluer inside R of about 10 arcsec. Structural parameters indicate that the mass-to-luminosity ratio ranges from 3 to 5.

Lee, Myung G.↗
NASA NTRS1993

BVRI CCD photometry of the resolved galaxy NGC 1560

BVRI CCD photometry of about 600 stars in the resolved spiral galaxy NGC 1560 is presented. The V - (B - V) diagram shows a dominant group of significantly reddened blue plume stars consisting of young massive main-sequence and evolved blue supergiant stars. The V luminosity function of the blue plume stars is constructed. The internal reddening is estimated at 0.24 mag. The mean magnitudes of the three brightest blue and red stars are obtained and a distance of 2.5 +/- 0.1 Mpc is obtained from four distance estimates.

Lee, Myung G.↗
NASA NTRS1993

Electronic Catalog Of Extragalactic Objects

NASA/IPAC Extragalactic Database (NED) is publicly accessible computerized catalog of published information about extragalactic observations. Developed to accommodate increasingly large sets of data from surveys, exponentially growing literature, and trend among astronomers to take multispectral approach to astrophysical problems. Accessible to researchers and librarians.

Helou, George↗
NASA NTRS1992

New Cepheid distances to nearby galaxies based on BVRI CCD photometry. III - NGC 300

A true distance modulus of (m - M) sub 0 = 26.66 +/- 0.10 mag (corresponding to 2.1 +/- 0.1 Mpc) has been determined for the Sculptor Group spiral galaxy NGC 300. New CCD data have been obtained for a sample of known Cepheids in this galaxy from which apparent distance moduli at B, V, R, and I wavelengths are determined. Combining the data available at different wavelenghts, and assuming a true distance modulus to the LMC of 18.5 mag, a true distance modulus is obtained for NGC 300, corrected for the effects of interstellar reddening. The availability of a new distance to NGC 300 brings to five the total number of galaxies with new CCD photometry of Cepheids, useful for calibration of the Hubble constant.

Freedman, Wendy L.↗
NASA NTRS1992

The reddening to the galaxy IC 342 from CCD BV photometry of its brightest stars

An attempt was made to estimate the reddening for the galaxy IC 342 on the basis of CCD BV photometry obtained for 117 stars brighter than V = 22.0 mag in a field centered near a spiral arm. At V = 19.4 mag, the plume of the main sequence and slightly evolved blue supergiant stars were detected. The plume is centered at a color of (B-V) = 0.54 mag. A comparison with similar color-magnitude-diagram data for the brightest stars in IC 1613 suggests that these stars in IC 342 are reddened by E(B-V) = 0.79 +/- 0.05 mag (A sub B = 3.32 +/- 0.21 mag).

Madore, Barry F.↗
NASA NTRS1992

Dynamics of the young LMC cluster NGC 1866

The 1.0-m telescope at Las Campanas was used to obtain V-band CCD images of the young LMC cluster NGC 1866 out to a projected radius of 100 pc. Radial velocities with a mean precision of 1.0 km/s were measured for 69 member supergiants using the echelle spectrograph on the 2.5-m telescope. The total cluster luminosity is 6.5 +/-0.3 x 10 exp 5 solar luminosities. A star-subtracted, median-filtered U frame was employed to determine photometric shape parameters. The stellar radial velocities indicate that NGC 1866 has a systemic velocity of 301.2 +/-1.0 km/s. A comparison of the derived values for NGC 1866 and the theoretical nu-0/sigma-0 - epsilon relationship indicates that the observed flattening is consistent with rotation. The quality of the fits for models with rotation is clearly superior to those without, and isotropic orbits agree best with the data in both cases.

Fischer, Philippe↗
NASA NTRS1991

The Cepheid distance scale

Developments concerning the period-luminosity (PL) relation for classical Cepheids are discussed with particular emphasis on the fact that Cepheids continue to provide the most homogeneous and reliable set of distances to many nearby galaxies. Observational programs relating to extragalactic Cepheids are also reviewed, and new distances and reddenings to individual galaxies are determined from these data using multiwavelength PL relations, based for the first time on self-consistent calibrating data sets. Three recent promising secondary extragalactic distance indicators (Tully-Fisher, planetary nebula luminosity functions, and surface-brightness fluctuations) tie their zero points to the Cepheid distance scale and give globally consistent values for the Hubble constant of about 80 km/sec/Mpc. Tying the Faber-Jackson relation and the supernova distance scales to the Leo and Virgo clusters yields similar results. Such a value for the Hubble constant is marginally inconsistent with new estimates of the ages of globular clusters, and it may prove to be a serious problem for standard cold-dark-matter models of the universe.

Madore, Barry F.↗
NASA NTRS1991

New Cepheid distances to nearby galaxies based on BVRI CCD photometry. II - The local group galaxy M33

A true distance modulus to the nearby spiral galaxy M33 has been determined based on CCD photometry obtained at BVRI wavelengths. M33 is presently one of five nearby galaxies used in the calibration of the IR Tully-Fisher relation, and thereby in the determination of the Hubble constant. Using period-luminosity relations at several wavelengths offers the advantage that the distance moduli derived can be corrected for the effects of interstellar extinction. These data indicate that there is internal reddening affecting the Cepheid photometry in M33 which must be accounted for if a true distance modulus is to be obtained for this galaxy. Adopting a true distance modulus to the LMC of 18.5 mag, the new CCD data yield a true distance to M33 of 24.64 + or - 0.09 mag, corresponding to a linear distance of 840 kpc. A mean value of the total color excess (foreground and internal) for the Cepheids in M33 is estimated to be E(B - V) = 0.10 + or - 0.09 mag, assuming a value for the total mean LMC Cepheid color excess of 0.10 mag.

Freedman, Wendy L.↗
NASA NTRS1991

Baade-Wesselink radii for NGC 1866 Cepheids

Radial velocities and CCD photometry suitable for a Baade-Wesselink analysis are now available for six short-period Cepheids (HV12198, HV12199, HV12202, HV12203, HV12204, and V4) in the LMC cluster NGC 1866. As a prerequisite for such an analysis, O-C diagrams have been constructed and examined for seven of the NGC 1866 Cepheids (HV12197, HV12198, HV12199, HV12200, HV12202, HV12203, and HV12204), yielding improved periods and estimates of the rate of period change in these coeval variables. One star, HV12198, shows possible evidence for period change, but the phase mismatch due to that change is small enough to have negligible effect on its Baade-Wesselink radius. The computed radii are in good agreement with the Baade-Wesselink, theoretical and cluster/association period-radius relations of Fernie (1984) and the Galactic relation of Coulson and Caldwell (1989). The Flower (1977) color-effective temperature relation and the Becker et al. (1977) mass-luminosity relation lead to mean masses of 4.9 + or - 0.5 solar masses and 4.6 + or - 0.5 solar masses for the respective metallicities of (Y,Z) = (0.0273,0.0016) and (0.026,0.02). Pulsation constants are also computed for these stars.

Cote, Patrick↗
NASA NTRS1991

The variable stars of NGC 1866

A search has been conducted for new variables in the LMC cluster NGC 1866 using new multiepoch CCD photometry. Eight previously unknown Cepheid variables, most near the cluster core, are found. Of the new variables reported by Storm et al. (188), only six of 10 appear to be Cepheids and one of these is not a member. Periods and mean magnitudes and colors for sufficiently uncrowded variables are reported, as is one red giant variable of long period and one Cepheid which is a single-lined spectroscopic binary with a velocity semiamplitude greater than or equal to 10.5 km/s. The variation of light-curve amplitude with position in the instability strip is reported along with an apparently nonvariable star, which is a radial velocity member, in the strip. A true distance modulus of 18.57 + or - 0.01 mag is obtained for the cluster.

Welch, Douglas L.↗
NASA NTRS1991

Computing and data processing

The applications of computers and data processing to astronomy are discussed. Among the topics covered are the emerging national information infrastructure, workstations and supercomputers, supertelescopes, digital astronomy, astrophysics in a numerical laboratory, community software, archiving of ground-based observations, dynamical simulations of complex systems, plasma astrophysics, and the remote control of fourth dimension supercomputers.

Smarr, Larry↗
NASA NTRS1990

An empirical test for the metallicity sensitivity of the Cepheid period-luminosity relation

The results are reported of the first observational test of the sensitivity of the zero point of the Cepheid period-luminosity relation to metal abundance. BVRI time-averaged observations of Cepheids in three radially separated and chemically different fields in M31 are used to find mean reddenings and true distance moduli that differ by only 0.25 mag. Consistent distances are found for all three fields. The large observed differences in the apparent moduli can be totally attributed to different mean extinctions among the three fields.

Freedman, Wendy L.↗