Absolute Visual Magnitude Research Articles

Cometary capture and the nature of the impactors

Abstract The inclination-averaged capture probability from nearly parabolic orbits to Halley-type orbits with periods P < 200 years and q < 1.5 AU is 0.0128 for an isotropic long-period source flux with perihelion distances q < 4 AU. The observed near-parabolic flux brighter than visual absolute magnitude H 10 = 7 is approximately 0.2 comets AU −1 a −1 , and the dynamical lifetime of the captured Halley-type comets is on the order of 0.3 Ma. The predicted steady-state number of such comets is thus about 3000, many times more than the number of observed Halley-type comets. Provided that long-period comets do not totally disintegrate during the capture process (e.g. into streams of small bodies such as cometary meteoroids and dust), this indicates that there should be a large population of undiscovered Halley-type ‘asteroids’ in the inner Solar System. The predicted number of dark Halley-type objects is sufficient to produce a terrestrial cratering rate comparable with that from observed near-Earth asteroids, and hence could explain the reported Galactic signal seen in the geological and biological records. The assessment of the terrestrial impact hazard should consider the possibility that a significant number of dark Halley-type objects may exist.

The Distance, Absolute Magnitude and Space Motion of Alpha Orionis

Alpha Orionis (Betelgeuse) is the brightest, and presumably the nearest, of the M-type supergiants. It is also one of the least reddened. These features make it important for the calibration of the absolute magnitudes and intrinsic colors of M supergiants. However, its distance has been difficult to establish, and there has been considerable debate concerning its reddening.The Hipparcos parallax for α Ori is 7.63 ± 1.64 mas, corresponding to a distance of 131 ± 30 pc and a true distance modulus (m — M)o of 5.59 ± 0.48 mag. If we adopt <V> = 0.50 and E(B - V) = 0.05, the mean absolute visual magnitude becomes <Mv> = -5.24, a result consistent with a luminosity classification of lab.The CN strength of α Ori measured in the near infrared also indicates luminosity class Iab. Furthermore, the star’s absolute magnitude at 1.04 μm, for the Hipparcos distance, is -8.34, in agreement with the M2 Iab supergiants in h &. χ Per for a distance modulus of (m — M)o = 12.0.From the Hipparcos proper-motion components and distance and a published radial velocity, we derive a space motion of 27.8 km s-1 with components U = +19.7, V = -7.3, and W = -1.5 km s-1 with respect to the Sun. This motion is not very different from the local standard of rest. It seems unlikely that μ Ori, at a distance only one-third that of the Trapezium, is physically associated with the Orion Complex.At 131 pc, the observed optical angular diameter of μ Ori, 0.055 arcsec, translates to a linear diameter of 7.2 AU. Centered on the Sun, itsphotosphere would be in the asteroid belt. Its angular diameter measured bythe Hubble Space Telescope in the UV (corresponding to the size of the chromosphere) is a factor of 2 larger. Surface features detected interferometrically are believed to be ~ 10% of the diameter in extent, corresponding to 0.7 AU or 108 km.

The Distances and Absolute Magnitudes of Some Well-Known Red Variables

Distances and absolute magnitudes have been obtained from an early distribution of Hipparcos data for a number of well-known late-type variables. These data were requested in 1981 in order to ensure that these important stars were not excluded from the Input Catalogue on account of their variability or very red color.Measurements were requested for 20 Mira variables, and 14 of these were successfully observed. Of these, the nearest to the Sun were found to be R Leo (at 102 pc), χ Cyg (106), R Cas (107), R Car (128), T Cep (210),and R Aql (211), with formal errors ranging from ±12 to ±57 pc. Mira itself was not considered because the presence of a companion causes an 11-month wobble in its photocenter which is likely to lead to a spurious parallax. The absolute visual magnitudes of Miras at mean maximum range approximately from -2.5 to +2.0 with a clear dependence on spectral type (cooler stars being fainter). This trend is reversed for absolute magnitudes in the near infrared.Results are also given for 10 small-amplitude variables of late type. The nearest of these are L2 Pup (M5 III, 61 pc) and R Dor (M8e, 62pc). The symbiotic star CH Cyg lies at a rather uncertain distance of 268 ± 65 pc.Data were obtained for 23 carbon stars, including the brightest representatives of each of several subgroups. The nearest of these was found to be the SRb variable U Hya, at 162 ± 20 pc. The stars 19 Psc, Y CVn, W Ori, and HD 201626 were all found to be somewhat more than 200 pc away.

SPECTROSCOPIC AND PHOTOMETRIC ANALYSIS OF NOVAE: A NEW CLASSIFICATION METHOD

ABSTRACT This study deals with the relationship between the absolute visual magnitude at maximum and the rate of decline (MMRD or Mv -- t3) for classical novae. Considering the most reliable data including the nebular expansion parallax method for 24 galactic novae, we find that there are two distinct kinds of galactic novae. Slopes of very fast and fast novae were found from a least-squares fit to their MMRD relation. The values of these two slope angles are similar. A similar result was found for moderately fast and slow novae, whose mean slopes differ by only a small amount. Therefore very fast novae can be grouped with fast novae, and moderately fast novae can be grouped with slow novae, so that we have only two separate novae groups. These two groups of novae are distinguished from each other by the Eddington luminosity. Our conclusions agree well with those of Duerbeck (1981, PASP, 93, 165), based on the light curves of approximately 100 galactic novae. Considering numerical nova model calculations (Livio 1992, ApJ, 393, 516), it seems that there is a good agreement between the observed and the theoretical MMRD relation. Moreover, we applied the same classification method to novae in M31 (Massimo and Livio, 1995, ApJ, 452, 704), and found the same two separate groups. We also determined expansion parallaxes for QZ Aur, V1974 Cyg, FH Ser, XX Tau, RW UMi, and QU Vul, and expansion velocities for Nova Aql 1995, V1974 Cyg and FH Ser. These results were found from H-alpha imaging and spectroscopic observations made by the author and A.Bianchini and T.Iijima (University of Padova), using the 1.82- and 1.22-m telescopes at the Ekar and Asiago Observatories. When we compare our images with those in the literature, we can obtain expansion parallaxes for QU Vul, QZ Aur, V1974 Cyg, and RW UMi. Shell diameters in the light of H-alpha for QU Vul, QZ Aur, V1974 Cyg and RW UMi were found to be 0.82, 0.83, 0.76 and 2.94 arcsec, respectively (epoch 1994-5). The literature gives nebular expansion parallaxes for 22 galactic novae. To these we can now add expansion parallaxes for QZ Aur and QU Vul, thus increasing the number to 24. Two high-dispersion spectra of FH Ser and N Aql 1995, and a low-dispersion spectrum of V1974 Cyg, give the following expansion velocities: 425 ± 25, 675 ± 25, and 1600 ± 100 km/s, respectively. (c) Society of

Spectral Classification of the 30 Doradus Stellar Populations

An optical spectral classification study of 106 OB stars within the 30 Doradus Nebula has sharpened the description of the spatial and temporal structures among the associated clusters. Five distinct stellar groups are recognized: (1) the central early-O (Carina phase) concentration, which includes Radcliffe 136 (R136); (2) a younger (Orion phase) population to the north and west of R136, containing heavily embedded early-O dwarfs and IR sources, the formation of which was likely triggered by the central concentration; (3) an older population of late-O and early-B supergiants (Scorpius OB1 phase) throughout the central field, whose structural relationship, if any, to the younger groups is unclear; (4) a previously known, even older compact cluster 3' northwest of R136, containing A- and M-type supergiants (h and χ Persei phase), which has evidently affected the nebular dynamics substantially; and (5) a newly recognized Sco OB1-phase association, surrounding the recently discovered luminous blue variable (LBV) R143, in the southern part of the Nebula. The intricacy of this region and the implications for the interpretation of more distant starbursts are emphasized. The evidence indicates that the formation of the 30 Dor stellar content was neither instantaneous nor continuous, but rather that the stars formed in discrete events at different epochs. The average difference between the derived and calibration absolute visual magnitudes of the stars is 0.05, indicating that the classification, calibration, and adopted distance modulus (V0 - MV = 18.6) are accurate. For 70 of the stars, either the absolute value of that difference is ≤0.6 mag, or they are subluminous dwarfs or superluminous supergiants. Many astrophysically interesting objects have been isolated for further investigation. Surprisingly, in view of the presence of several O3 supergiants, the mid-Of star R139 is identified as the most massive object in this sample; it is located well along the 120 M☉ track, very near the Humphreys-Davidson limit, and it is probably an immediate LBV precursor. This work can and should be extended in three ways: (1) higher resolution and higher S/N observations of many of the stars with larger ground-based telescopes for quantitative analysis, (2) ground-based spectral classification of the numerous additional accessible stars in the field, and (3) spatially resolved spectral classification of compact multiple systems with the Hubble Space Telescope.

On the Revision of Radiometric Albedos and Diameters of Asteroids

A simple, approximate method is presented for the recalculation of asteroid diameters and geometric albedos given new, improved absolute visual magnitudes. This method avoids recourse to detailed models of an object's reflected and thermally emitted flux components. Its basis is the assumption that for small changes in absolute magnitude the quantity (1 − A V ) D 2can be considered invariant, where A V and Dare the object's Bond albedo and diameter, respectively. The usefulness of the method for revising the diameters and albedos of asteroids, especially those covered by the IRAS Minor Planet Survey(E. F. Tedesco, Ed., 1992, Tech. Rep. PL-TR-92-2049, Phillips Laboratory, Hanscom AFB, MA), is demonstrated by applying it to a number of objects for which recently updated absolute magnitudes are available.

Proper motions, absolute magnitudes and spatial distribution of Zirconium stars

AbstractThe computational algorithm to determine the the proper motions of Zirconium stars on the basis of catalogues “Carte du Ciel” and on the recent photographic observations carried out with the 70cm Abastumani meniscus telescope is presented. It allowed to determine the proper motions of 288 stars in the region around α Per with a rms error of ± 0,004 arcsec/yr. Applying the method proper motions of 74 Zirconium stars and 146 control stars have been obtained. The error of proper motions obtained for the North Zone (δ > −2°) 109 AGK3 control stars is ± 0.006 arcsec/yr.On the basis of proper motins absolute magnitudes were separately calculated for the MCLPZS and LASZS.For the MCLPZS the average absolute visual magnitude at maximum, corresponding to the mean period of P = 350 days, equals −3ϕm.9. For the LASZS the mean absolute visual magnitude, corresponding to the apparent median ones equals −1ϕm.9. Low luminosity (Mv = −1ϕmϕ9) Zirconium stars escape rather far (at a distance of up to 2 kpc) to the South from the Galactic plane into the region l ∼ 240 – 260°, where its assumed to be a connection with the Large Magellanic Cloud (LMC) begins to appear. Low luminosity Zirconium stars are weakly correlated with position of the Galaxy spiral arms. The MCLPZS show a somewhat other distribution.

THE PHYSICAL PROPERTIES OF THE SX PHOENICIS STAR CY AQUARII

ABSTRACT Photometry of CY Aqr in the uvby-Beta and VRIC photometric systems has been secured and analyzed. A phase-averaged effective gravity of log geff = 4.04 and effective temperature of 7740 K are found from model-atmosphere grids. The star is metal poor with a derived [Fe/H] = -1.5. A mass of 1.06 solar mass is found from the analysis, the radius is 1.59 R and absolute visual magnitude is MV = 2.5m.

Photometry of the RR Lyrae Variable U Comae

view Abstract Citations (4) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometry of the RR Lyrae Variable U Comae Heiser, A. M. Abstract UBV and uvby observations of U Comae, an RR Lyrae c-type variable with a premaximum "bump," have been used to determine an improved pulsation period and an estimated distance. The ephemeris for U Com, derived from all the photoelectric observations, is: Max HJD=2441336.9679+0.2927386iE. The distance to U Com, between 1400 and 1650 pc depending on the value of the absolute visual magnitude of the RR Lyrae c variables, indicates that it is either a thick disk object or a halo variable. A comparison of these observations with first overtone pulsation models indicates that U Com has an Teff of about 7250° and a log g of about 3.1, if the variable's [Fe/H] is -1.32. Publication: The Astronomical Journal Pub Date: November 1996 DOI: 10.1086/118169 Bibcode: 1996AJ....112.2142H Keywords: STARS: VARIABLES: RR LYRAE; STARS: INDIVIDUAL: U COMAE full text sources ADS | data products SIMBAD (9)

Orbital elements for double stars of Population II. The system HD 29907

For HD 29907 results are presented from radial-velocity monitoring and from photometric observations on the uvby system. The object is a binary system at a distance of around 50 parsecs from the sun. The primary component is a G2 VI star. The secondary component remains unidentified. The absolute visual magnitude of the primary component is MV=+6.6, and the effective temperature and abundance of heavy elements are given by and [Fe/H]=-1.7, respectively. The V magnitude appears variable with a range of at least 0.12 magnitudes. Colour indices appear stable. The system has a radial velocity of , an orbital period of 29.9 days and an eccentricity of 0.41. The total space velocity with respect to the galactic center is 340 and the object approaches escape velocity.

Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations. III. CV MON in Anon Van Den Bergh

view Abstract Citations (6) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations. III. CV MON in Anon Van Den Bergh Gieren, Wolfgang P. ; Mermilliod, Jean-Claude ; Mathews, Jaymie M. ; Welch, Douglas L. Abstract As part of a program aimed at comparing the galactic Cepheid distance scales from cluster ZAMS fitting and from independent Baade-Wesselink techniques, we have used new, high-quality light and radial velocity curves of the Cepheid CV Mon supposed to be a member of the sparse cluster Anon van den Bergh to obtain its distance and mean radius from the visual surface brightness method. We find the distance to CV Mon to be 2160±200 pc which is ∼20% larger than the ZAMS-fitting distance to the cluster determined by Turner [JRASC, 72, 248 (1978)] but cluster membership of CV Mon is still possible given the uncertainties of both determinations. Our surface brightness analysis yields a mean radius of 53.5±3.9 Rsun for CV Mon. The Cepheid's absolute visual magnitude is -3.67±0.36 mag, whose large uncertainty is dominated by the relatively uncertain absorption correction. Use of near infrared photometry would reduce the uncertainty in the absolute magnitude. We find rather clear evidence that CV Mon is pulsating in the fundamental radial mode. There is no evidence, neither from the existing photometry nor from radial velocity observations obtained over eleven years, that there is a binary companion to the Cepheid. Publication: The Astronomical Journal Pub Date: May 1996 DOI: 10.1086/117941 Bibcode: 1996AJ....111.2059G Keywords: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL; GALAXIES: DISTANCES AND REDSHIFTS; CEPHEIDS full text sources ADS | data products SIMBAD (2) Related Materials (2) Part 1: 1994AJ....107.2093G Part 2: 1995AJ....110.2280M

Recent observations of the WR central star of the planetary nebula LMC-N66

The recent evolution of the central star of the planetary nebula LMC-N66 is presented. Before 1987, it showed a weak continuum with aTeff≥120 000 K andLbol≈25 000L⊙ and in a few years it developed strong WR features (P Cygni line profiles in N v at 124.0 nm and C IV at 155.0 nm, wide Heii emission, etc.) typical of a WN 4.5. Additionally the stellar continuum increased by a large factor and the absolute visual magnitude of the star changed from + 1.24 in 1987 to−2.57 in January, 1995. The WR features and enhanced continuum, evidencing a powerful mass-loss event remained with small variations for more than 5 years. Recent ultraviolet and optical data shows that the mass-loss seems to have diminished abruptly in the last three months.

The Extremely Low Luminosity White Dwarf ESO 439−26

We present a detailed analysis of the extremely low luminosity white dwarf ESO 439-26. The measured trigonometric parallax of π = 00237 ± 00030, together with the observed V magnitude of 20.52, yields an absolute visual magnitude of MV = 17.4 ± 0.3. ESO 439-26 thus lies more than 1 mag faintward of the observed cutoff of the white-dwarf luminosity function in the Galactic disk and could therefore be the coolest and hence oldest white dwarf ever detected. However, we show from a detailed analysis of the optical energy distribution that the intrinsic low luminosity of ESO 439-26 is the result of its small radius, or large mass. Our best solution is reached with Teff = 4560 ± 100 K, log g = 9.04 ± 0.14, and a pure-helium atmospheric composition. Evolutionary models are used to derive a mass of M = 1.21 ± 0.07 M☉ and a cooling age of 6.4 ± 0.3 Gyr, a value that is smaller than the current estimates of the age of the Galactic disk.

PHOTOMETRIC CALIBRATION OF HYDROGEN- AND HELIUM-RICH WHITE DWARF MODELS

ABSTRACT Bolometric corrections and color indices on various photometric systems are provided for an extensive grid of hydrogen- and helium-rich white dwarf model atmospheres. Absolute visual magnitudes, masses, and ages are also obtained for each model from detailed evolutionary cooling sequences appropriate for these stars. The results of our calculations are briefly compared with published observational material. These calculations can easily be extended to any given photometric system.

The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics

view Abstract Citations (564) References (69) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics Reid, I. Neill ; Hawley, Suzanne L. ; Gizis, John E. Abstract The Third Catalogue of Nearby Stars (Gliese & Jahreiss Preliminary Version of the third Catalogue of Nearby Stars, 1991) includes over 1850 stars which lie north of δ 30° and are either identified as spectral type M, or are unclassified but with an absolute visual magnitude estimate MV>+8.O. Although there is no uniformity in selection criteria, and many of the stars lack basic data (radial velocities, spectral types, accurate photometry), the observational properties of these stars underlie most estimates of the fundamental characteristics of the Galactic Disk. We have obtained optical spectroscopy of 1746 of the 1876 stars-the remaining 130 are binary companions of brighter stars and inaccessible to our observations. These spectra allow us, first, to exclude 61 stars as either degenerates or as misclassified earlier-type (B - K) stars lying beyond the 25 pc limit; to establish radial velocities accurate to ±10 km s-1 for all stars confirmed as late-type dwarfs; to determine spectral types and absolute magnitudes from the TiO bandstrength, allowing more accurate distance estimates for stars with inaccurate (or no) trigonometric parallax measurements; and to identify stars with Ha emission (chromospherically active stars) and with strong CaH absorption (perhaps including some metal-poor disk subdwarfs). We have determined the nearby-star luminosity function from complete samples derived by applying both the distance limits defined by Wielen (1974) and by using limits derived from our own analysis. In both cases, we find good agreement with Wielen's results to MV ∼+11, but lower densities at the maximum (MV∼+12). The latter analysis results in a luminosity function, ΦCNS, which closely matches photometric parallax analyses for MV<+11 and MV>+14 -- we do not recover the apparent excess of low-luminosity stars inferred from analysis of the 5 pc sample. However, ΦCNS does lie below Φphot at the peak (MV∼12), and we suggest that this offset is caused by the inclusion of unrecognized binaries in the photometric surveys. We have also reanalyzed the local stellar kinematics using the complete sample and find that the velocity distributions show significant departures from single Gaussian velocity dispersions. Publication: The Astronomical Journal Pub Date: October 1995 DOI: 10.1086/117655 Bibcode: 1995AJ....110.1838R Keywords: STARS: FUNDAMENTAL PARAMETERS; SURVEYS; STARS: PECULIAR; STARS: LUMINOSITY FUNCTION full text sources ADS | data products SIMBAD (1848) CDS (2) Related Materials (2) Catalog: 1997yCat.3198....0R Part 2: 1996AJ....112.2799H

MAP-based Trigonometric Parallaxes of ALTAIR and VEGA

view Abstract Citations (11) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS MAP-based Trigonometric Parallaxes of ALTAIR and VEGA Gatewood, George ; de Jonge, Joost Kiewiet Abstract Trigonometric parallaxes for stars in the regions of the nearby main-sequence A stars Altair and Vega are derived from data collected with the Multichannel Astrometric Photometer (MAP) and associated Thaw refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of all trigonometric studies of Altair is now +0".1963±0".00077, corresponding to a distance modulus of 1.465±0.009 mag and an absolute visual magnitude of 2.22±0.012. Altair's diameter is 1.63±0.08 solar diameters. The weighted mean trigonometric parallax of all trigonometric studies of Vega is now 0".1300±0".00077, yielding a distance modulus of 0.570±0.013 and an absolute visual magnitude of 0.60±0.013. Vega's diameter is 2.68 + 0.06 solar diameters. The apparent motion of both stars is linear over the period of observation, strongly suggesting the absence of short-period (1-6 yr) stellar or brown dwarf companions to either star. We also find a parallax of 0".0155±0".0006 for the high proper motion F8 reference star BD +38°3231. The derived luminosity, UV excess, and high space motion of this star all indicate that it is a subdwarf. Publication: The Astrophysical Journal Pub Date: September 1995 DOI: 10.1086/176146 Bibcode: 1995ApJ...450..364G Keywords: STARS: DISTANCES; STARS: INDIVIDUAL NAME: ALTAIR; STARS: INDIVIDUAL NAME: VEGA; STARS: FUNDAMENTAL PARAMETERS; STARS: LOW-MASS; BROWN DWARFS full text sources ADS | data products SIMBAD (5)

The Minimum Ejection Velocity of Calcium in Type I[CLC]a[/CLC] Supernovae and the Value of the Hubble Constant

Evidence is presented for a relation between the visual absolute magnitudes of Type Ia supernovae (SN Ia's) and their minimum ejection velocities of calcium as indicated by the red edge of the Ca II H and K absorption blend in moderately late-time spectra. Independent calibrations of the relation by means of (1) the Cepheid-based distance to NGC 5253, the parent galaxy of SN 1972E, and (2) light-curve calculations based on hydrodynamic models of SN Ia's, give low H0, near 60 km s-1 Mpc-1.

Absolute Magnitudes and Colors of A-F Supergiants from Near-Infrared Features. II. The Galactic Sample

view Abstract Citations (13) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absolute Magnitudes and Colors of A-F Supergiants from Near-Infrared Features. II. The Galactic Sample Slowik, Donald J. ; Peterson, Deane M. Abstract In this paper we extend the calibration of the infrared oxygen triplet at λ7774 Å as a luminosity indicator in A and F supergiants. We add five members of southern Galactic clusters to the nine northern objects previously considered, and find them completely consistent with the earlier relations. The result is a substantially improved fit between equivalent width and absolute visual magnitude. We reconsider the error estimates of the colors, and particularly, reduce our estimates of the errors in the colors of the northern objects. An increase in the estimated intrinsic dispersion in absolute magnitude of these objects about the mean relation, to about 0.50 mag, follows directly from the decrease in the estimated uncertainty in the reddening corrections. We also reconsider the problem of estimating intrinsic color using our measure of the infrared Ca II triplet strength. Again, the added data increase the quality of the calibration. Several techniques developed in the literature for estimating colors are compared with the Ca II indicator, and found to be less accurate, or, if comparable, costly in observing time. Further, we have looked at the issue of contamination by undetected companions. Use of IUE archives provided only one example among our sample, an object whose duplicity had been previously reported. We argue that crowding is infrequent and easily detected in the majority of cases. Toward an understanding of the nature of this equivalent width- absolute magnitude relation, we show that LTE model atmospheres adequately predict the ultraviolet, visible and near-infrared colors and H features of our sample. This is an important check against significant departures from the thin ("plane-parallel") approximation for the atmospheres of these high luminosity objects, and from LTE in the hydrogen atom. However, this test does not include the most luminous of these objects, which may still require more sophisticated treatment. Publication: The Astronomical Journal Pub Date: May 1995 DOI: 10.1086/117445 Bibcode: 1995AJ....109.2193S Keywords: STARS: GIANTS; STARS: FUNDAMENTAL PARAMETERS full text sources ADS | data products SIMBAD (28) MAST (1)

The blue anbd visual absolute magnitude distributions of Type IA supernovae

view Abstract Citations (79) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Blue and Visual Absolute Magnitude Distributions of Type IA Supernovae Vaughan, Thomas E. ; Branch, David ; Miller, Douglas L. ; Perlmutter, Saul Abstract Tully-Fisher (TF), surface brightness fluctuation (SBF), and Hubble law distances to the parent galaxies of Type Ia supernovae (SNs Ia) are used in order to study the SN Ia blue and visual peak absolute magnitude (M_B_ and M_v_) distributions. We propose two objective cuts, each of which produces a subsample with small intrinsic dispersion in M. One cut, which can be applied to either band, distinguishes between a subsample of bright events and a smaller subsample of dim events, some of which were extinguished in the parent galaxy and some of which were intrinsically subluminous. The bright events are found to be distributed with an observed dispersion of 0.3 <~σ_obs_(M) <~0.4 about a mean absolute magnitude (M^bar^_b_ or M^bar^_v_). Each of the dim SNs was spectroscopically peculiar and/or had a red B - V color; this motivates the adoption of an alternative cut that is based on B - V rather than on M. To wit, SNs Ia that are both known to have -0.25 <B - V < +0.25 and not known to be spectroscopically peculiar show observational dispersions of only σ_obs_(M_B_) = σ_obs_(M_V_) = 0.3. Because characteristic observational errors produce σ_err_(M) > 0.2, the intrinsic dispersion among such SNs Ia is σ_int_(M) <= 0.2. The small observational dispersion indicates that SNs Ia, the TF relation, and SBFs all give good relative distances to those galaxies that produce SNs Ia. The conflict between those who use SNs Ia in order to determine the value of the Hubble constant (H_0_) and those who use TF and SBF distances to determine H_0_ results from discrepant calibrations. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175196 Bibcode: 1995ApJ...439..558V Keywords: Data Reduction; Stellar Magnitude; Supernovae; Astronomical Photometry; Astronomical Spectroscopy; Color-Color Diagram; Color-Magnitude Diagram; Distance; Hubble Constant; Spectrum Analysis; Astrophysics; COSMOLOGY: DISTANCE SCALE; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products NED (96) SIMBAD (91)

Spectral observations of red dwarfs II. New observations of flare stars in the Pleiades cluster region

We studied the spectra of 24 flare stars of the Pleiades cluster region obtained on the 2.6m telescope of the Byurakan observatory in the years 1986–1989. From the spectral indices of titanium oxide (TiO) and other chemical elements of the stars investigated we determined their spectral classes and luminosities (absolute visual stellar magnitudes). The agreement of these moduli of the stars with the distance modulus of the Pleiades cluster confirms that 21 of them belong to the cluster. Only three of them (FSP 169, FSP 377, and FSP 435) are possibly not members of the cluster. This indicates that the flare activity of a star is a reliable criterion for its membership in a nearby stellar system (cluster or association).