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The Gemini North Adaptive Optics (GNAO) facility is the upcoming AO facility for Gemini North providing a state-of-the-art AO system for surveys and time domain science in the era of JWST and Rubin operations. GNAO will be optimized to feed the Gemini infrared Multi Object Spectrograph (GIRMOS). While GIRMOS is the primary science driver for defining the capabilities of GNAO, any instrument operating with an f/32 beam can be deployed using GNAO. The GNAO project includes the development of a new laser guide star facility which will consist of four side-launched laser beams supporting the two primary AO modes of GNAO: a wide-field mode providing an improved image quality over natural seeing for a 2-arcminute circular field-of-view and a narrow-field mode providing near diffraction-limited performance over a 20x20 arcsecond square field-of-view. The GNAO wide field mode will enable GIRMOS's multi-IFU configuration in which the science beam to each individual IFU will be additionally corrected using multi-object AO within GIRMOS. The GNAO narrow field mode will feed the GIRMOS tiled IFU configuration in which all IFUs are combined into a "super"-IFU in the center of the field. GNAO also includes the development of a new Real Time Controller, a new GNAO Facility System Controller and finally the development of a new AO Bench. We present in this paper an overview of the GNAO facility and provide a status update of each product., SPIE conference 2022 Montreal

The citizen Continental-America Telescopic Eclipse (CATE) Experiment was a new type of citizen science experiment designed to capture a time sequence of white-light coronal observations during totality from 17:16 to 18:48 UT on 2017 August 21. Using identical instruments the CATE group imaged the inner corona from 1 to 2.1 RSun with 1.″43 pixels at a cadence of 2.1 s. A slow coronal mass ejection (CME) started on the SW limb of the Sun before the total eclipse began. An analysis of CATE data from 17:22 to 17:39 UT maps the spatial distribution of coronal flow velocities from about 1.2 to 2.1 RSun, and shows the CME material accelerates from about 0 to 200 km s−1 across this part of the corona. This CME is observed by LASCO C2 at 3.1–13 RSun with a constant speed of 254 km s−1. The CATE and LASCO observations are not fit by either constant acceleration nor spatially uniform velocity change, and so the CME acceleration mechanism must produce variable acceleration in this region of the corona.

PurposeThe purpose of this paper is to report on one high school English‐language‐learner's (ELL) breadth and depth of vocabulary as he communicated with his teacher through e‐mail across geographic boundaries for over 18 months.Design/methodology/approachThe authors began by separating 358 e‐mails into three time periods (first beginning, second middle, and third end) to calculate breadth using lexical density (type‐token ratios). Then, we sampled e‐mails based on personal and impersonal topics within these time periods and linguistically analyzed them for lexical cohesion, semantic usage, and derivational morphology. Interviews with participants before and after the analysis served as member checks.FindingsThe quantitative results showed a steady improvement in the breadth of the student's vocabulary over time. Qualitative analyses revealed four major uses of vocabulary within the context of e‐mail and the teacher‐student relationship.Practical implicationsGiven our findings, we offer educators insights into ELL strategies and vocabulary assessment, not only with e‐mail but in all written communication.Social implicationsA social writing tool like e‐mail can be useful for learning English in a safe, non‐threatening environment. Moreover, a trusting social relationship between communicators that develops over time can expedite the language learning process.Originality/valueVery few studies have looked at the strategic ways ELL students use vocabulary to learn English through e‐mailing.

We describe the design and performance of a near-infrared camera for use at the University of Wyoming 24 inch telescope at Red Buttes Observatory. The camera makes use of a HAWAII-2 2048 × 20482048×2048 pixel HgCdTe array, sensitive from 0.9–2.5 μm. The array is operated with a Generation III controller from Astronomical Research Cameras and makes use of a General Use Multi-Channel Preamplifier from IRLabs. The camera optics consist of a compact 1:1 re-imaging Offner relay with a cold pupil mask and includes a nine-position filter wheel driven internally with a cryogenically conditioned steppermotor. The primary objective was to develop a low-cost system for testing the HAWAII-2 array and electronics that were acquired for a larger project, while at the same time providing a temporary near-infrared camera for use at Red Buttes Observatory. In this article we present various aspects of the mechanical construction, optics, electronics, and performance.

We report improved transformation equations between the u'g'r'i'z' and UBVRCIC photometric systems. Although the details of the transformations depend on luminosity class, we find a typical rms scatter on the order of 0.001 mag if the sample is limited to main-sequence stars. Furthermore, we find that an accurate transformation requires complex, multicolor dependencies for the bluer bandpasses. Results for giant stars will be reported in a subsequent paper.

We present the most recent results of an optical survey of the position error contours ("error boxes") of unidentified high energy gamma-ray sources., Comment: 1 figure, 3 tables, to be published in Astronomical Journal

Wide-field (20' × 20') UBVI images of intermediate-redshift (z = 0.39), Butcher-Oemler cluster Cl 0024+1654 have been obtained. These data probe the rest-frame mid-UV properties over a much larger area than previous studies of Cl 0024+1654. Using these data, a multicolor catalog of nonstellar objects, assumed to be galaxies, has been constructed and analyzed. Using statistical arguments, the observed galaxy sample is separated into field and cluster populations. The basic photometric properties of these populations are presented and discussed. The "dropout" objects (i.e., objects undetected in one or more photometric bands) in our catalog are also discussed. A description of the final UBVI images, as well as the object catalog, is provided in an appendix. In a second appendix the use of SExtractor in crowded fields, such as the core of Cl 0024+1654, is discussed. The specific issues of the mid-UV properties of red envelope cluster galaxies, as well as the possible detection of a faint blue cluster population, are discussed in a forthcoming companion paper by Silva, Alexov, & Pierce.

ABSTRA C T We report the discovery of 42 red supergiant variables (RSVs) in the late-type spiral galaxy M101. Periods for the luminosity variation of these RSVs were determined from 20 epochs of ground-based CCD photometry in the Kron‐Cousins R band obtained with the KPNO 2.1-m and WIYN 3.5-m telescopes over a span of three years. The periods found were in the range 200‐1300 days. Using the relationship between the RSV periods and their luminosity in the Kron‐Cousins I band, we estimate a reddening-corrected distance modulus to M101 of 29:40 ^ 0:16 mag (based on a distance modulus of 18:5 ^ 0:1 mag for the Large Magellanic Cloud). This distance is consistent with the Hubble Space Telescope Key Project Cepheid distances of 29:34 ^ 0:17 mag for the outer field of M101 and 29:21 ^ 0:17 mag for the inner field.

ABSTRA C T We present CCD photometry of red supergiant long-period variables (LPVs) in the Per OB1 association, the Large Magellanic Cloud (LMC) and M33. The photometry was obtained in the Kron‐Cousins R and I bandpasses and in a narrow bandpass (l0a 8250 A; FWHMa 300 A) chosen to avoid TiO bands in the spectral energy distribution of the LPVs. Because the strength of the TiO bands varies greatly with temperature, which varies with the phase of an LPV, avoiding TiO reduces the amplitude of the photometric variations seen in LPVs. The result is a lower dispersion and a well defined period‐luminosity (PL) relation. For the LMC sample we find an rms dispersion of 0.27 mag in the narrow-band PL relation and slightly larger dispersions for the LPVs in Per OB1 and M33. This dispersion is comparable to that of the Cepheid PL relation at similar wavelengths. Adopting a distance modulus of 18:5 ^ 0:1 mag for the LMC, we obtain distance moduli of 11.68^0.15 mag for Per OB1 and 24:85 ^ 0:13 mag for M33. These distances agree well with those based on main sequence fitting for Per OB1 and the Cepheid distance for M33. Since LPVs are , 5 times more common than Cepheids and have a well defined PL relation, LPVs provide a promising method for estimating Galactic and extra galactic distances.

The distance to the Virgo cluster of galaxies, a primary rung on the ladder to establishing the distance scale of the Universe, 14.9 ± 1.2 Mpc, has been determined through ground-based observations of Cepheid variables in NGC4571. This agrees very well with other modern distance estimates, and the extragalactic distance scale now seems established. Based on this distance, a Hubble constant of H0 = 87 ± 7 km s -1 Mpc -1 has been calculated.

The Virgo and Fornax clusters of galaxies play central roles in determining the Hubble constant H_0. A powerful and direct way of establishing distances for elliptical galaxies is to use the luminosities of the brightest red-giant stars (the TRGB luminosity, at M_I = -4.2). Here we report the direct observation of the TRGB stars in a dwarf elliptical galaxy in the Virgo cluster. We find its distance to be 15.7 +- 1.5 Megaparsecs, from which we estimate a Hubble constant of H_0 = 77 +- 8 km/s/Mpc. Under the assumption of a low-density Universe with the simplest cosmology, the age of the Universe is no more than 12-13 billion years.

We have identified 230 Tycho-2 Spectral Catalog stars that exhibit 8 micron mid-infrared extraphotospheric excesses in the MidCourse Space Experiment (MSX) and Spitzer Space Telescope Galactic Legacy MidPlane Survey Extraordinaire (GLIMPSE) surveys. Of these, 183 are either OB stars earlier than B8 in which the excess plausibly arises from a thermal bremsstrahlung component or evolved stars in which the excess may be explained by an atmospheric dust component. The remaining 47 stars have spectral classifications B8 or later and appear to be main sequence or late pre-main-sequence objects harboring circumstellar disks. Six of the 47 stars exhibit multiple signatures characteristic of pre-main-sequence circumstellar disks, including emission lines, near-infrared K-band excesses, and X-ray emission. Approximately one-third of the remaining 41 sources have emission lines suggesting relative youth. Of the 25 GLIMPSE stars with SST data at >24 microns, 20 also show an excess at 24 microns. Three additional objects have 24 micron upper limits consistent with possible excesses, and two objects have photospheric measurements at 24 microns. Six MSX sources had a measurement at wavelengths >8 microns. We modeled the excesses in 26 stars having two or more measurements in excess of the expected photospheres as single-component blackbodies. We determine probable disk temperatures and fractional infrared luminosities in the range 191 < T < 787 and 3.9x10^-4 < L_IR/L_* < 2.7x10^-1. We estimate a lower limit on the fraction of Tycho-2 Spectral Catalog main-sequence stars having mid-IR, but not near-IR, excesses to be 1.0+-0.3%., Accepted to ApJ

Spitzer Space Telescope imaging as part of the Galactic Legacy Mid-Plane Survey Extraordinaire (GLIMPSE) reveals a previously unidentified low-latitude rich star cluster near l=31.3 degrees, b=-0.1 degrees. Near-infrared JHK' photometry from the Wyoming Infrared Observatory indicates an extinction of A_V ~ 15+/-3 mag for cluster members. Analysis of 13CO features along the same sightline suggests a probable kinematic distance of 3.1 -- 5.2 kpc. The new cluster has an angular diameter of ~1-2 pc, a total magnitude m_{K_0}=2.1 corrected for extinction, and a luminosity of M_K ~ -10.3 at 3.1 kpc. In contrast to young massive Galactic clusters with ages, Accepted for Publication in AJ Report with full resolution images available at http://physics.uwyo.edu/~chip/Glob

We present evidence for non-Gaussian velocity fields within the cores of luminous elliptical galaxies. This evidence is based upon high signal-to-noise, medium-resolution spectroscopy of the cores of early-type members of the Virgo and Coma clusters obtained with the WIYN 3.5-m telescope. The Virgo data were acquired using an integral-field unit (DensePak) allowing the velocity field to be sampled over a variety of spatial scales. The Coma data were obtained through single, 2-arcsec diameter fibers. The cross-correlation profiles of luminous ellipticals show considerable structure, often having several features with amplitudes as high as 10% that of the cross-correlation peak itself. This structure is most obvious within a radius of 1.5 arcsec (at Virgo), or < 100 pc, and is nearly undetectable when the data are binned over R < 15 arcsec, or < 1 kpc. Similar features are found in the single-fiber spectra of the luminous ellipticals in the Coma Cluster suggesting they are ubiquitous to giant ellipticals. Interesting, only the most luminous elliptical galaxies show this phenomena; the central regions of lower luminosity ellipticals have regular, Gaussian-like profiles. We interpret this kinematic structure as ``stellar streaming'' and suggest that this phenomena could be a relic signature of the merger history of luminous elliptical galaxies., Latex, 5 pages, 2 figures

The correlation between the luminosities and rotation velocities of galaxies can be used to estimate distances to late-type galaxies. It is an appropriate moment to re-evaluate this method given the great deal of new information available. The major improvements described here include: (a) the template relations can now be defined by large, complete samples, (b) the samples are drawn from a wide range of environments, (c) the relations are defined by photometric information at B,R,I and K' bands, (d) the multi-band information clarifies problems associated with internal reddening, (e) the template zero-points are defined by 24 galaxies with accurately known distances, and (f) the relations are applied to 12 clusters scattered across the sky and out to velocities of 8,000 km/s. The biggest change from earlier calibrations are associated with point (e). Roughly a 15% increase in the distance scale has come about with the five-fold increase in the number of zero-point calibrators. The overall increase in the distance scale from the luminosity--linewidth methodology is about 10% after consideration of all factors. Modulo an assumed distance to the Large Magellanic Cloud of 50 kpc and no metallicity corrections to the Cepheid calibration, the resulting value of the Hubble Constant is H0 = 77 +- 8 km/s/Mpc where the error is the 95% probable statistical error. Cummulative systematic errors internal to this analysis should not exceed 10%. Uncertainties in the distance scale ladder external to this analysis are estimated at 10%. If the Cepheid calibration is shifted from the LMC to NGC 4258 with a distance established by observations of circum-nuclear masers then H0 is larger by 12%., 34 pages including 15 figures and 1 table. One 14 page landscape table not encapsulated. Paper accepted for publication in Astrophysical Journal

We describe a new approach for the determination of cosmological parameters using gravitational lensing systems with multiple arcs, exploiting the fact that a given cluster can produce multiple arcs from sources over a broad range in redshift. The coupling between the critical radius of a single arc and the projected mass density of the lensing cluster can be avoided by considering the relative positions of two or more arcs. Cosmological sensitivity appears through the angular size-redshift relation. We consider simulated data constructed using a more general form for the potential, realistic sources, and an assumed cosmology and present a method for simultaneously inverting the lens and extracting the cosmological parameters. The input data required are the image and measured redshifts for the arcs. The technique relies upon the conservation of surface brightness in gravitationally lensed systems. We find that for a simple lens model our approach can recover the cosmological parameters assumed in the construction of the simulated images., AAS Latex. 19 pages, 9 postscript figures

Magnitude-limited samples of spiral galaxies drawn from the Ursa Major and Pisces clusters are used to determine their extinction properties as a function of inclination. Imaging photometry is available for 87 spirals in B,R,I and K' bands. Extinction causes systematic scatter in color-magnitude plots. A strong luminosity dependence is found. Relative edge-on to face-on extinction of up to 1.7 mag is found at B for the most luminous galaxies but is unmeasurably small for faint galaxies. At R the differential absorption with inclination reaches 1.3 mag, at I it reaches 1.0 mag, and at K' the differential absorption can in the extreme be as great as 0.3 mag. The luminosity dependence of reddening can be translated into a dependence on rotation rate which is a distance-independent observable. Hence, corrections can be made that are useful for distance measurements. The strong dependence of the corrections on luminosity act to steepen luminosity-linewidth correlations. The effect is greatest toward the blue, with the consequence that luminosity-linewidth slope dependencies are now only weakly a function of color., Comment: 23 pages, 5 figures

The Ursa Major Cluster has received remarkably little attention, although it is as near as the Virgo Cluster and contains a comparable number of HI-rich galaxies. In this paper, criteria for group membership are discussed and data are presented for 79 galaxies identified with the group. Of these, all 79 have been imaged at B,R,I bands with CCDs, 70 have been imaged at K' with a HgCdTe array detector, and 70 have been detected in the HI 21cm line. A complete sample of 62 galaxies brighter than M(B)=-16.5 is identified. Images and gradients in surface brightness and color are presented at a common linear scale. As has been seen previously, the galaxies with the reddest global colors are reddest at the centers and get bluer at large radii. However, curiously, among the galaxies with the bluest global colors there are systems with very blue cores that get redder at large radii., A LATEX file without figures. The postscript version (7.1Mb in gzipped format) including all the tables, figures and scanned versions of the plates can be retrieved as preprint no.208 from http://www.astro.rug.nl:80/~secr/ Accepted for publication in The Astronomical Journal

Near-infrared photometric measurements for 131 Northern Galactic Cepheids are presented. The Cepheid light curves are sampled with an average of 22 measurements per star fully covering the phase of each Cepheid. The J, H, and K light curves for each Cepheid were uniformly interpolated to find the intensity mean magnitudes within each band. The results are consistent within ±1% for 26 stars in common with previous studies. This paper is the first in a projected series of two papers which will provide additional fundamental data for Cepheids in the Galaxy, namely, NIR photometry and line-of-sight extinction. In the course of this project, 93 additional variables were fortuitously observed within the Cepheid program fields, 82 of which have previously not been identified.

The velocity dispersion of Cygnus OB2 was incorrectly quoted in the original manuscript as V 1⁄4 2:44 0:07 km s 1 for Vavg (the weighted average heliocentric velocities), and V 1⁄4 3:41 0:11 km s 1 for Vmid (the averages of the largest and smallest heliocentric velocities). The FWHM values for the Gaussian fits in Figure 23 are also incorrectly quoted as 5:70 0:17 km s 1 and 8:01 0:26 km s 1 for Vavg and Vmid, respectively. The correct one-dimensional velocity dispersions and corresponding FWHM values, as indicated by the Gaussian fits to the data in Figure 23, are V 1⁄4 5:74 0:15 km s 1 (Vavg), FWHM 1⁄4 13:50 0:36 km s 1 (Vavg), V 1⁄4 8:03 0:26 km s 1 (Vmid), and FWHM 1⁄4 18:87 0:60 km s 1 (Vmid). These values are larger than typical OB associations and open clusters (1Y2.5 km s 1; Bate & Bonnell, MNRAS, 356, 1201 [2005]). The larger dispersion estimates may be attributed to the uncertain systemic velocities of binaries (both identified and unidentified), owing to the limited orbital phase information from the current data set. The Astrophysical Journal, 681:735, 2008 July 1

We present new ground-based high-resolution images of 23 blue galaxies whose membership has been confirmed spectroscopically in the two distant rich clusters Abell 370 and Cl 0024+1654. The images, taken with the High Resolution Camera on the CFHT, have a stellar FWHM=0.45 arcsec. Ten of these blue galaxies are found to have close companions, with separations on the scale of 1 to 2 arcsec. These multiple systems represent 45% of the confirmed blue galaxy population in the two clusters. Several of the remaining blue galaxies also have peculiar morphologies and features, such as tidal tails, suggestive of interactions/mergers

We review seven of the most reliable indicators used for deriving distances to galaxies as far way as 100 Mpc: globular-cluster luminosity functions (GCLF), novae, Type Ia supernovae (SN Ia), H I-line-width relations, planetary-nebula luminosity functions (PNLF), surface-brightness fluctuations (SBF), and fundamental-plane relationships for elliptical galaxies (Dn - sigma). In addition, we examine the use of Cepheid variables since these serve to set zero points for most of the methods. We pay particular attention to the uncertainties inherent in these methods, both internal and external. We then test these uncertainties by comparing distances derived with each technique to distances derived from surface-brightness fluctuations. We find that there are small systematic offsets between the PNLF, GCLF, and SBF methods, with the PNLF and GCLF distances being on average 6% and 13% larger than those of the SBF method. The dispersion between the PNLF and SBF distances is 8%; the GCLF-SBF dispersion is 16%, the SN Ia-SBF dispersion is 28%, Dn-sigma-SBF dispersion is 26%, and the Tully-Fisher-SBF dispersion is 32%. The latter value drops to 14%, however, when one considers only well-mixed groups, suggesting that the spiral galaxies measured with Tully-Fisher are not always spatially coincident with the groups' elliptical galaxies. In the mean, all the methods agree extremely well. We also present a summary of distances to the Virgo Cluster. Weighted and unweighted averages of the seven methods yield Virgo distances of 16 ± 1.7 and 17.6 ± 2.2 Mpc, respectively. The overlap among all the indicators is well within the expected accuracies of the methods. Using the weighted or unweighted Virgo distances to bootstrap to the Coma Cluster, we find the Hubble constant to be either 80 ± 11 or 73 ± 11 km s-1 Mpc-1 respectively.

Deep, high-resolution images (FWHM=0″.43) of a relatively face-on, late-type spiral galaxy (NGC 4571) in the Virgo Cluster have been obtained using the High-Resolution Camera (HRCam) and the Canada-France-Hawaii Telescope. The galaxy is apparently resolved into stars. The combined image has a limiting magnitude of m R ∼26, enabling the brightest three magnitudes of the luminosity function to be examined, where the photometry is complete. Point-spread function fitting photometric techniques (i.e., DAOPHOT) are applied to the data allowing the application of quantitative and objective criteria for distinguishing stars from H II regions and compact clusters/associations

The absolute magnitudes derived for supernovae of type Ia in spiral galaxies depend critically on their assumed intrinsic colors. For 14 SNIa in spirals (and an assumed Hubble parameter of 75 km s-1 Mpc-1) one finds that MBmax = -20.02 ± 0.17 if (B-V)max = -0.25. This may be compared to MBmax = -18.97 ± 0.28 for seven SNIa in E and S0 galaxies which were assumed to have been unreddened. For (B-V)max = -0.25 SNIa in spirals are thereafter 1.05 ± 0.32 mag more luminous than those in E and S0 galaxies. However, this difference is reduced to 0.30 ± 0.30 mag if (B-V)max = 0.00 is adopted. It follows that SNIa are good standard candles only if (B-V)max 0.0, in which case they are relatively faint at MBmax -19.0. If they are blue with (B-V)max -0.25 then they exhibit different luminosity distributions, with MBmax -20.0 in spirals and MBmax = -19.0 in E and S0 galaxies. The Hubble diagram for the absorption-corrected maximum magnitudes of SNIa is found to have marginally smaller dispersions for a Virgocentric infall model than it does for a model without such infall.

Supporting material for the article of Shaya et al. (1992, ApJ) is presented. One table gives measured galaxy distances used to construct a map of observed peculiar velocities, and another table gives a grid of the distribution of light used to construct a map of expected peculiar velocities. A preferred model was developed which gave a best fit between these maps, and this model has been used to generate output kinematic distances which are recorded here for groups and individual galaxies with V 0 < 3000 km/s

I-band CCD photometry and K-band NICMOS photometry of the brightest red supergiants in IC 4182 (UGC 8188) are presented in order to estimate the distance to this galaxy. Assuming that the brightest red supergiants are «standard candles» and adopting an absolute calibration of the brightest red supergiants, a distance modulus of 27.0 ± 0.2 mag (2.5 ± 0.3 Mpc) is obtained. This estimate is more than a magnitude closer in distance modulus than using photographic V-band photometry and a similar absolute calibration

Multicolor CCD photometry is presented for a sample of 15 spiral and irregular members of the Local, Sculptor, and M81 groups with M B ≤ -16.0 and relevant as potential calibrators of the luminosity-line width relations. The sample contains those galaxies for which a ground-based study of Cepheid variables could provide accurate distances and hence an absolute calibration for the relations. Unfortunately, only six of the systems presently have reliable independent distance estimates, but this number is sufficient to provide a reasonable calibration

Les images CCD en bande B de 230 galaxies des amas Virgo et Ursa Majoris sont analysees. Les correlations entre l'etat poussiereux et la luminosite des galaxies sont etudiees.

Morphological classifications of 231 galaxies in and near the Virgo and Ursa Major clusters are reported which show that luminosity classification techniques (LCTs) can be used to determine the luminosities of spiral galaxies with an accuracy of about 0.7 mag on CCD frames. The observations in the direction of the Virgo Cluster confirm the assignment of some galaxies to the background field, strongly confirming that the large dispersion in the Tully-Fisher relation for Virgo galaxies is at least partly due to contamination of the Virgo core sample by background galaxies. LCTs yield a distance of 15.3 + 2.6 or - 2.2 Mpc for the spiral and irregular galaxies associated with the core of the Virgo Cluster proper. The Ursa Major and Virgo cluster distances are found to be the same. A class of galaxies with fuzzy, anemic outer structure and active star formation in their cores is found to be common in Virgo but rare in the Ursa Major Cluster. 31 refs.

From purpose and scope: This report includes a description of the geohydrologic features of the different aquifers; a definition of source, occurrence, movement, and quality of the ground water; and an estimation of the current pumpage and ground-water storage.

The great success of the Hubble-Sandage system of galaxy classification indicates that galaxies as a whole are remarkably similar. As a result, the global properties of galaxies have proven to be extremely useful as diagnostic tools for examining their stellar and gaseous content. This fortunate occurrence has allowed the formulation of the Tully-Fisher (T-F) relationships for estimating the distances to galaxies (Tully and Fisher 1977; Aaronson et al. 1979). The difference in the slopes of the blue and infrared Tully-Fisher relations implies that correlations must exist between color and 21-cm line width as well as color and absolute magnitude (Tully et al. 1982).

CCD images taken in the B, R, and I passbands have revealed substantial stellar ovals in the interior region (about 1 kpc) of the two nearby Sc galaxies M51 and M100. The amplitude of the azimuthal intensity variation is found to be 25 percent and 45 percent, respectively. The ovals are associated with both noncircular streaming motions and enhanced star formation. Blue (B - I about 0.8) rings of star formation are found near the outer boundary of the ovals. The close association of the star-forming rings and the ovals with the estimated position of the galaxy's inner Lindblad resonance (ILR) suggests a dynamical connection between the ovals and the ILR. Interestingly, M100 possess both an inner oval (within the ILR) and a classical bar (extending to near the expected radius for corotation). 48 references.

La photometrie CCD de galaxies spirales dans les amas du Virgo et Ursa Major est presentee et combinee avec des mesures precises de largeurs de raie HI a 21 cm afin d'etudier les relations Tully-Fisher comme un indicateur de distance. Il existe une dependance faible des relations TF avec le type morphologique. La dispersion intrinseque des relations TF est tres petite et, avec les corrections d'inclinaison et d'extinction appropriees, ces relations fournissent des distances avec une tres grande precision pour une etendue vaste d'environnements de galaxies. Les distances aux amas Ursa Major et Virgo, etablies par une calibration des relations TF a partir de 3 galaxies proches sont respectivement 15,5±1,2 Mpc et 15,6±1,5 Mpc. Des estimations du champ de vitesse virgocentrique ont permis de calculer une valeur de la constante de Hubble Ho=85±10 km s −1 Mpc −1