Ultraviolet Color Research Articles

Ultraviolet Photometry from the S2/68 Observations in the TD1 Satellite

SummaryAn ultraviolet photometric system based on observations obtained from the ultraviolet Sky Survey Telescope in the TD1 satellite is described. The system considered here consists of ultraviolet magnitudes at λ1 = 2740A, λ2 = 2190A and λ3 = 1490A. The extinction free parameters derived from the observed ultraviolet colours enable determination of interstellar reddening, spectral type and luminosity. This photometric system has been evaluated by comparing these parameters with other classification parameters.

A DISCOVERY PROGRAM FOR BRIGHT QUASARS: PRELIMINARY RESULTS.

ABSTRACT A program has been undertaken to obtain a complete sample of bright quasars on the basis of ultraviolet color excess. Spectroscopic examination of candidates selected from two-color Schmidt telescope films has yielded four new quasars brighter than B = 16.5 mag, with the candidate list containing two more previously identified. Magnitudes, color indices, and redshifts are presented for the new discoveries, along with positions and finding charts. Although the sample is not yet complete, these first results suggest that bright quasars have a low surface density.

Ultraviolet Spectrophotometry of Early-Type Stars

The ultraviolet spectra of B stars obtained with the sky scan telescope in the TD1 satellite have been used to obtain narrow-band magnitudes at several wavelengths. These photometric bands have an effective half-width of 100 Å. We have proposed a two-dimensional classification scheme based on ultraviolet colours, and some preliminary results are presented.

A Discussion on astronomy in the ultraviolet - The Celescope survey and the galactic distribution of interstellar absorption

The Celescope experiment consisted of four 31 cm aperture telescopes equipped with digital television photometers, installed in the Orbiting Astronomical Observatory, launched 7 December 1968. We used this instrument to conduct a survey in four ultraviolet colours: U l (2100-3200 A), U2 (1550—3200 A), U3 (1350— 2150 A) and U4 (1050-2150 A). We have published the observational results in the Celescope catalog of ultraviolet stellar observations (Davis, Deutschman & Haramundanis 1973). I have studied these results, together with relevant ground-based data, to determine the distribution of interstellar dust and variations of the interstellar extinction law with the position in the galaxy. Results from the data contained in the Celescope catalogue have been prepared for publication (Peytremann & Davis 1974)- These results have now been refined and expanded to include new ground-based U, B, V, and H(3 photometry acquired at Kitt Peak National Observatory, as well as new observations by W. A. Deutschman and R. Schild at Cerro Tololo Inter-American Observatory

Stellar flux measurements of early-type stars in the 912-1075 Angtroms band.

view Abstract Citations (11) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar flux measurements of early-type stars in the 912 - 1075 Å band. Troy, B. E., Jr. ; Johnson, C. Y. ; Young, J. M. ; Holmes, J. C. Abstract Stellar flux measurements in the wavelength range 912-1075 A (A0 = 950 A) are presented for eight OB type stars. These measurements were obtained from two photometers aboard a rocket flown from White Sands, N.M., on 1971 October 8. The ultraviolet color index (m950 - V) derived from the flux values varies from approximately -6 to -4 between spectral classes O8 and B2. Radiation from B3 and later stars was below our detectable limit. The variation of the 950 A color index with spectral type is similar to, but steeper than, that of the 1115 A and 1376 A indices, and more negative in value. The derived color indices are consistently more negative than predictions from model atmosphere calculations. Subject headings: early-type stars - photometry - ultraviolet Publication: The Astrophysical Journal Pub Date: February 1975 DOI: 10.1086/153365 Bibcode: 1975ApJ...195..643T full text sources ADS | data products SIMBAD (9)

Ultraviolet television data from the orbiting astronomical observatory. II - Stellar ultraviolet colors and interstellar extinction

The results from the Celescope Catalog of Ultraviolet Stellar Observations (Davis, Deutschman, and Haramundanis 1973) are studied, emphasizing statistical groups and subgroups of stars. In spite of the rather large observational errors, the great number of Celescope observations make it possible to do that kind of study with reasonable accuracy. Some stars have ultraviolet colors that differ significantly from those of the group to which they have been assigned on the basis of ground-based observations. An attempt is made to describe the general properties of the ultraviolet colors of the stars as observed by the Celescope experiment on board NASA's Orbiting Astronomical Observatory (OAO-2). Besides the direct applicability of these results to the general study of stellar atmospheres and of interstellar extinction, they are also considered as a frame of reference for further studies of individual stars and groups of stars.

ULTRAVIOLET PHOTOMETRY OF THE SUPERNOVA (1972) IN NGC 5253

ABSTRACT The supernova (1972) in NGC 5253 was observed with the wide-band filter photometers of OAO-2 between 1972 May 20 and 1972 July 22. Initially the ultraviolet colors of the supernova resembled those of an F supergiant star. The last observations revealed that the 2460 A flux was greater than expected from a stellar photosphere. During the 63 days of OAO-2 observations we measured the energy radiated between 4250 A and 2460 A to be 2.9 x 1048 ergs. Only 30% of this energy was radiated shortward of 3320 A. From the OAO-2 observations and published ground-based data we estimate the minimum total radiated energy of the supernova to be 7 X 10 ergs. Key words: supernovae - ultraviolet photometry

Angular Diameters of Quasars of Unusual Colour

TWO neutral-coloured stellar objects, OH471 and OQ172, have been shown to be QSOs with redshifts of 3.40 and 3.53 respectively1,2. This has stimulated interest in other radio sources identified with stellar objects which lack the ultraviolet or blue colour excesses normally associated with quasars. Browne and McEwan3 have published a list of objects which, though blue, show no ultraviolet excess; I. W. A. B., J. H. Crowther and R. L. Adgie have prepared a list (unpublished) of sources identified with neutral coloured objects, which includes both OH471 and OQ172. Sources of both types have been put forward as possible high redshift QSOs. We have measured the radio angular diameter of the sources on both lists, and of four further objects which may possibly be similar. These objects4,5, OJ287, W Com, ON235 and BL Lac, show no spectral lines but resemble OH471 and OQ172 in colour.

Intrinsic ultraviolet colors from OAO-2 Celescope observations for stars on the main sequence

Intrinsic ultraviolet colors (Uj- v)o have been determined with ultraviolet magnitudes derived from several hundred observations taken with the photometers of OAO-2's Celescope experiment. Relationships between intrinsic ultraviolet color, (B- v)o, and spectral class are presented for main-sequence stars from B 0 to G 3. A brief description of the Celescope and its calibration is included, and a comparison of the determined colors is made with theoretical colors.

UBV Photometry of the Metal-Rich Globular Cluster NGC 6171

Three-colour ( UBV ) photographic photometry of stars in the globular cluster NGC 6171 is reported. The photometry is calibrated with a previously published photoelectric sequence and consists essentially of a revision and extension of an earlier colour–magnitude (C–M) diagram by Sandage and Katem, together with new ultra-violet measurements. The general character of the C–M diagram is unchanged, confirming the strong population of horizontal branch stars on the red side of the instability region, the large spread in colour on the red giant branch, possibly caused by the presence of asymptotic branch stars, and a small value of Δ V = 2.07 mag. However, the red horizontal branch is shifted redwards by about 0.15 mag from its position in the earlier C–M diagram, which did not take account of colour equation, and there is a clear separation of about 0.1 mag between the red end of the horizontal branch and the subgiant branch. Other non-uniformities in the stellar distribution along the horizontal branch are discussed, together with the extremely small dispersion in V magnitude found there. The photographic ultra-violet colours confirm the previously found small ultra-violet excess of the giant stars, with a final best value of δ ( U–B ) = 0.09 ± 0.03 mag at ( B−V ) 0 = 1.04. Some of the stars probably belonging to the asymptotic branch have smaller ultra-violet excesses than subgiant stars of the same colour. The red giant stars appear to be more concentrated towards the cluster centre than stars on the horizontal branch. In an Appendix, it is shown that such differences could be ascribed to a lower mass for stars on the horizontal branch, since the time of relaxation of stellar velocities near the centre of NGC 6171 is of the same order as the evolutionary time spent on the horizontal branch.

Intrinsic variations of interstellar extinction laws

The intrinsic ultraviolet colours of early type stars have been derived from the rocket data of J. W. Campbell and A. M. Smith. There exists a considerable spread in these colours. One possible source is the predicted rms variation due to the effect of rotation. It is necessary to recognise that rotation is an important source of uncertainty of the interstellar extinction curves derived from the comparison of pairs of stars. Predicted rms errors due to different sources (rotation, uncertainty of MK spectral type, photometric errors) have been compared with the dispersion of the observed extinction data and it is found that part of the large scatter could be due to intrinsic differences of the properties of interstellar grains.

Multicolor Photoelectric Photometry of Bright Galaxies. III

view Abstract Citations (103) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multicolor Photoelectric Photometry of Bright Galaxies. III Tifft, William Grant Abstract Four-color photoelectric data on 64 galaxies are presented and discussed; most of the galaxies lie in the region of the Virgo Cluster. Galaxies are divided into groups according to their photometric properties in the nuclear regions. Abnormally red and blue nuclei are found in both spiral and elliptical galaxies. Interstellar reddening and nuclear star formation appear to be involved. A strong concentration of nuclear anomalies is found in the core of the Virgo Cluster. Ultraviolet color variability is considered likely in the nucleus of M87. Color-magnitude diagrams for the two brightest magnitudes in the Virgo Cluster are presented and show a well-defined color-luminosity effect. Publication: The Astronomical Journal Pub Date: April 1969 DOI: 10.1086/110816 Bibcode: 1969AJ.....74..354T full text sources ADS | data products NED (69)

Stellar Photometry from a Satellite Vehicle

view Abstract Citations (61) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar Photometry from a Satellite Vehicle Smith, Andrew M. Abstract Data acquired from a satellite-borne telescope photometer sensitive to far-ultraviolet radiation are presented. The telescopic field of view was about ir square degrees; the effective photometer band width and wavelength were 204 and X 1376 A, respectively. With A v/E(B - V) = 3.1 and E(B - V) = 1 an average extinction at 1376 A of 10.7 + 0.6 mag was found from the data. An ultraviolet color index, (mi s - V), corrected for interstellar absorption was computed for 96 stars, and from these data together with a set of unblanketed model atmospheres the derivation of a temperature scale was attempted. The results indicate a scale from 2000 to 30000 K lower than currently estimated The effect of using a more appropriate line-blanketed model for these purposes is briefly discussed Publication: The Astrophysical Journal Pub Date: January 1967 DOI: 10.1086/148988 Bibcode: 1967ApJ...147..158S full text sources ADS | data products SIMBAD (96)

Photoelectric H-beta photometry for B stars in the Orion Belt region.

The parameter P, which measures empirically the HP absorption strength in a star spectrum, has been obtained for 93 stars in the belt region of Orion. On the basis of P and (U-B)0, the ultraviolet color index of the UB V system corrected for interstellar reddening, almost all these stars prove to be of nearly the same age and hence probably have absolute magnitudes nearly the same as for equivalent stars in the Scorpio-Centaurus group. The ambiguity discussed by Hardie, Heiser, and Tolbert (Astrophys. J. 140, 1472, 1964)-whether to have stars of the same age at different distances, or stars at the same distance of different ages-can best be explained in terms of the first alternative.

A sensitive photometric luntinositv discriminant for late-type dwarf and giant stars

view Abstract Citations (4) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A sensitive photometric luntinositv discriminant for late-type dwarf and giant stars Neff, John S. Abstract Filter photometry of late-type giants and dwarfs with intermediate bandpass interference filters located at 0.33, 0.37, 0.47, and 0.55 is presented. The locations of unreddened dwarfs and giants as well as little reddened supergiants on several two-color diagrams are shown. Giants and dwarfs later than CS on the MK system, with similar m.47-m.55 colors, can have ultraviolet colors .33- . that can differ by as much as 0W2 with the giants showing a deficiency relative to the dwarfs. It is suggested that late-type dwaris can be separated from giants by photometric observations of this type. Publication: The Astronomical Journal Pub Date: April 1966 DOI: 10.1086/109905 Bibcode: 1966AJ.....71..202N full text sources ADS | data products SIMBAD (3)

Color Anomalies and Metal Deficiencies in Solar-Type Disk Population Stars.

view Abstract Citations (4) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Color Anomalies and Metal Deficiencies in Solar-Type Disk Population Stars. Conti, Peter S. ; Deutsch, Armin J. Abstract Many solar-type stars of the disk population have spectral lines that are systematically weaker than those in the Hyades dwarfs of the same temperature. Small line-weakening has often been inferred from a photometric determination of, say, an ultraviolet color excess 8 (U-B), a low m, index, or some other comparable color anomaly. The line weakening is, in turn, usually attributed to a small metal deficiency. But a direct calculation shows that the small metal deficiencies which have been spectroscopically established in some of these stars can directly weaken the lines by far too little to produce the color anomalies observed. More than half the line absorption in the near ultraviolet and violet spectra of these stars is caused by lines that lie on the "flat" part of the curve of growth and that are very insensitive to small changes in abundance. However, the strengths of these saturated lines are directly proportional to the velocity parameter. In fact, the color anomalies observed among most solar-type stars appear to arise primarily from differences in turbulence. The correlations among line strengths, kinematics, and age imply that turbulence decays with age. High turbulence is responsible for a large part of the photometric anomalies that distinguish many metallic4ine stars. In these objects, however, duplicity also plays an important role in perturbing the photometric indices and in making them unreliable indicators of metallicism. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109655 Bibcode: 1965AJ.....70S.670C full text sources ADS |

Photoelectric Hβ Photometry for B Stars in the Orion Belt Region.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoelectric Hβ Photometry for B Stars in the Orion Belt Region. Crawford, D. L. Abstract The parameter p, which measures empirically the Hp absorption strength in a star spectrum, has been obtained for 93 stars in the "belt region" of Orion. On the basis of p and (U-B)0, the ultraviolet color index of the UB V system corrected for interstellar reddening, almost all these stars prove to be of nearly the same age and hence probably have absolute magnitudes nearly the same as for equivalent stars in the Scorpio-Centaurus group. The ambiguity discussed by Hardie, Heiser, and Tolbert (Astrophys. J. 140, 1472, 1964)-whether to have stars of the same age at different distances, or stars at the same distance of different ages~can best be explained in terms of the first alternative. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109656 Bibcode: 1965AJ.....70S.671C full text sources ADS |

New photoelectric observations of stars in the old galactic cluster M67

view Abstract Citations (269) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New photoelectric observations of stars in the old galactic cluster M 67. Eggen, O. J. ; Sandage, A. R. Abstract New photoelectric observations are given for 190 stars in and near M67. By using the properties of the (U - B, B - V) diagram it has been possible to separate the effects of interstellar reddening from those of line blanketing, and values of E(B - V) = +()N)6, E(U - B) = +(Y O4, A(B - V) = +()w()3, A(U - B) = +(YN)6 have been derived. The small value of the blanketing corrections, which indicates that the Fe/H abundance ratio is similar to that of the Sun and the Hyades cluster, shows that at least for some stars there has been very little eurichinent of heavy elements in the parent interstellar medium between the time of formation of M67 and the present. The color-magnitude diagram of the cluster shows the presence of a sharply defined gap on the rising branch of the evolved main sequence. This gap may represent a very rapid interlude on a gravitational time scale, between the depletion of the hydrogen in the stellar core and the firing of the hydrogen in a shell outside the core. Similar gaps are definitely present in NGC 2477 and NGC 752. The color-magnitude diagram of M67 also contains a horizontal branch populated by stars which are almost certainly cluster members on the basis of both the proper motions and the success with which the observed anomalies in their ultraviolet colors can be explained as a gravity effect. A comparison of evolutionary tracks, derived from a model by Hoyle, with the observed colormagnitude diagram gives good agreement except for a slight deviation near the main sequence caused by a more vertical rise to the evolved sequence than is predicted by theory. The distance modulus of M67, corrected for absorption, is m - M = 9".38 l 0"'2, obtained by using the method of the evolutionary deviation curve. Publication: The Astrophysical Journal Pub Date: July 1964 DOI: 10.1086/147901 Bibcode: 1964ApJ...140..130E full text sources ADS | data products SIMBAD (203) GCPD (1)

The Globular Cluster M5.

Photographic measures on B and V are given for over 1000 stars in the nearby globular cluster MS. Photoelectric measures on 69 stars yield accurate calibration to near V = 22 mag. in the color-magnitude diagram. Ultraviolet colors indicate that MS is unreddened ( = 0.014 + 0016 mag.). The intrinsic ultraviolet excess of the cluster is obtained accurately down onto the main sequence ( tU - B] = -0.22 mag) MS is indicated to be deficient in metals by only a factor of 17, as compared to the extreme cases of halo globular clusters, which are deficient by a factor of over 200. Line blanketing is discussed and corrected for. The MS main sequence is then fitted in the Mb ), log T plane to a Hyades main sequence with evolution. The uncertainties are discussed, and a final estimate of Mv = +06 + 0 2 mag. is suggested for cluster cepheids like those in M3, MS, and RR Lyrae itself. If the evolutionary models of Haseigrove and Hoyle are fitted, an age of 20 X 10 years + 20 per cent is obtained. Recent computations by Woolf on the available energy supply in horizontal branch stars, however, indicate only about half this age is the maximum permitted Woolf's smaller age agrees better with the age of the universe as inferred from tile expansion of the nebulae.

A Study of Some Early Type Close Binary Stars.

view Abstract Citations (55) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of Some Early Type Close Binary Stars. Abhyankar, K. D. Abstract A study of spectroscopic and photometric material for three binaries has supplied additional evidence regarding dynamical interaction between their components. 1. Scorpii. A new orbit of the primary confirms the apsidal motion found by earlier workers. The velocity for the secondary is 40 km/sec positive with respect to that of the primary; at least part of the difference is real. X 4471 of He I and X 4553 of Si III are about twice as strong when the secondary is approaching as when the secondary is receding. H shows smaller changes in the opposite direction. Changes in line intensities and the difference between i and WI are attributed to gaseous matter projected against the approaching side of the secondary. Measured difference in the magnitudes of the two components indicates that the secondary is overluminous. 2. HD 47129.-Combining new observations with the old, a correct period of 14.3961 days is , and a new orbit of the primary is obtained. The measures of secondary lines show large scatter, difference in Wi and WI, and a velocity amplitude smaller than the primary. Systematic changes in velocity- curves and line intensities from one epoch to the next are also noted. At phases around 7.2 days, the secondary lines are stronger by 3040 per cent; hydrogen lines in the primary spectrum are fuzzy and have negative velocities with respect to the mean for all lines. The spectral types of the two components are alike, but the strength of the red He I lines indicates a strong red continuum for the secondary. Analysis of the shell lines gives a mean distance of the circumstellar envelope from the center of the primary equal to six times the radius of the star. Variations in the number of absorbing atoms in the envelope in different directions and from cycle to cycle are indicated. The electron temperature of the shell is 240000, the electron density is 1.7 x l0'1/cc, and the mass density is about 3.3 X l() lI gm/cc. The He/H abundance ratio in the primary is normal. The distance of the star is about 1140 parsecs. 3. A 0 Cassiopeiae.-Comparison of a new spectroscopic orbit with earlier orbits gives definitive values of Wi = -31.1 + 0.07 km/sec and e = 0.035 + 0.004. K1 and K2 seem to vary from epoch to epoch. Apsidal motion with a period of 70 years is found. Observations of the secondary are widely scattered, but they do not indicate any real difference between the W velocities of the two components. The velocity amplitude of the secondary is smaller than that of the primary. Photometric light-curves in yellow, blue, and ultraviolet colors show asymmetries and negative reflection effects. The observed primary minimum is shifted by -0.67 day with respect to the computed phases. Irregular fluctuations of light of the order of 0.03 mag. are superposed on the smooth variation of the light of the primary. Publication: The Astrophysical Journal Supplement Series Pub Date: April 1959 DOI: 10.1086/190047 Bibcode: 1959ApJS....4..157A full text sources ADS | data products SIMBAD (18)