UBV Magnitudes Research Articles

Insights into the Evolution of Five Isolated Galaxies

Abstract Galaxy evolution is believed to be conditioned by the environment. Isolated galaxies or galaxies in poor groups are an excellent laboratory to study evolutionary mechanisms where effects of the environment are minimal. We present new Swift-UVOT data in six filters, three in the ultraviolet (UV), of five isolated galaxies aiming at shedding light into their evolution. For all of our targets, we present new UV integrated fluxes, and for some of them also new UBV magnitudes. Our observations allow us to improve their multiwavelength spectral energy distributions, extending them over about three orders of magnitude in wavelength. We exploit our smooth particle hydrodynamical simulations with chemo-photometric implementation anchored, a posteriori, to the global multiwavelength properties of our targets, to give insight into their evolution. Then we compare their evolutionary properties with those previously derived for several galaxies in groups. The evolution of our targets is driven by a merger that occurred several gigayears ago, in the redshift range 0.5 ≤ z ≤ 4.5, not unlike what we have already found for galaxies in groups. The merger shapes the potential well where the gas is accreting, driving the star formation rate and the galaxy evolution. Isolated galaxies should not have suffered from interactions for at least 3 Gyr. However, the initial merger is still leaving its signature on the properties of our targets. Several rejuvenation episodes, triggered by in situ accretion, are highlighted. Moreover, jellyfish morphologies appear as these galaxies achieve their maximum star formation rate, before their quenching phase.

Variability of the planetary nebula NGC 6572 and its central star during the interval covered by optical observations

Estimates of relative line intensities available in the literature and integrated Hβ fluxes of the planetary nebula NGC 6572 during the time covered by optical observations (1938–2013) are compared to search for possible variations. Line intensities measured from observations obtained at the Crimean Station of the Sternberg Astronomical Institute in 2013 are presented, as well as previously unpublished photographic spectroscopic data obtained 1972–2005. Our analysis of all the available data shows that the line intensities do not vary within the observational uncertainties, with the possible exception of the [OIII] 4959 and 5007 A lines, which show a tendency for their intensity increase with time. This can be interpreted as a manifestation of a temperature increase of the central star, or radial stratification of the [OIII] emission in the nebula, with the latter explanation being less probable. However, stratification is clearly visible in the [OII] and [NII] line intensities. The integrated Hβ flux is most probably constant at F(Hβ) = (1.50 ± 0.03) × 10−10 erg cm−2 s−1. A refined estimate of the interstellar extinction toward NGC 6572 has been obtained from radio and optical data, c(Hβ) = 0.42 ± 0.03. The MAST spectroscopy data were used to derive the central star’s UBV magnitudes in 2004. Integrated photoelectric UBV observations of the nebula and central star for 1971–2005 are presented.

THE CORRELATION BETWEEN Hα EMISSION AND VISUAL MAGNITUDE DURING LONG-TERM VARIATIONS IN CLASSICAL Be STARS

H\alpha\ equivalent widths and UBV magnitudes are calculated for Be star disk models that grow in size and/or density with time. We show that these simple models are consistent with the known Be star classes of positive and inverse correlations between long-term variations in H\alpha\ and V magnitude as identified by Harmanec. We support the conclusion of Harmanec that the distinction is controlled by the inclination of the disk to the line of sight. We demonstrate that the strength of these correlations, particularly those of an inverse correlation where the system becomes fainter as the H\alpha\ emission strength grows, is strongly influenced by the scale height of the inner Be star disk and the extent of the gravitational darkening of the central B star due to rapid rotation. This dependence may allow coordinated spectroscopic and photometric observations to better constrain these poorly known Be star parameters.

The photometric system of the Tsinghua-NAOC 80-cm telescope at NAOC Xinglong Observatory

The Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at the Xinglong Observatory of NAOC, with the main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations taken on 12 photometric nights, spanning the period from 2004 to 2012, we derived an accurate transformation equation between the instrumental ubvri magnitudes and standard Johnson UBV and Cousins RI magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at the Xinglong Observatory became gradually worse over the period from 2005 to 2012 (e.g., ∼21.4 mag vs. ∼20.1 mag in the V band).

V2368 Ophiuchi: an eclipsing and double-lined spectroscopic binary used as a photometric comparison star for U Ophiuchi

The A-type star HR 6412 = V2368 Oph was used by several investigators as a photometric comparison star for the known eclipsing binary U Oph but was found to be variable by three independent groups, including us. By analysing series of new spectral and photometric observations and a critical compilation of available radial velocities, we were able to find the correct period of light and radial-velocity variations and demonstrate that the object is an eclipsing and double-lined spectroscopic binary moving in a highly eccentric orbit. We derived a linear ephemeris T min.I = HJD (2454294.67 +/- 0.01) + (38.32712 +/- 0.00004)d x E and estimated preliminary basic physical properties of the binary. The dereddened UBV magnitudes and effective temperatures of the primary and secondary, based on our light- and velocity-curve solutions, led to distance estimates that agree with the Hipparcos distance within the errors. We find that the mass ratio must be close to one, but the limited number and wavelength range of our current spectra does not allow a truly precise determination of the binary masses. Nevertheless, our results show convincingly that both binary components are evolved away from the main sequence, which makes this system astrophysically very important. There are only a few similarly evolved A-type stars among known eclipsing binaries. Future systematic observations and careful analyses can provide very stringent tests for the stellar evolutionary theory.

Notices to investigation of symbiotic binaries V. Physical parameters derived from UBV magnitudes

In the optical, the spectrum of symbiotic binaries consists of contributions from the cool giant, symbiotic nebula and the hot star. Strong emission lines are superposed on the continuum. In this paper we introduce a simple method to extract individual components of radiation from photometric UBV magnitudes. We applied the method to classical symbiotic stars AX Per, AG Dra, AG Peg and Z And, the symbiotic novae RR Tel and V1016 Cyg and the classical nova V1974 Cyg during its nebular phase. We estimated the electron temperature and emission measure of the nebula in these systems and the V magnitude of the giant in the symbiotic objects. Our results are in a good agreement with those obtained independently by a precious modelling the UV-IR SED.

Parameters of galactic early B supergiants

Context. The interstellar extinction, E(B - V), of OB supergiants is usually derived from the observed color index, (B - V), in comparison with the intrinsic one. This method works properly only if the stellar wind does not influence the optical continuum emission. Over the past years, many OB supergiants have been found to have wind-velocity distributions with rather high β values; i.e., their winds are only slowly accelerating, resulting in relative density enhancements within the wind-continuum forming region. It has been found that these kinds of winds might indeed influence the total continuum emission even at optical wavelengths. Aims. We investigate the influence of the wind on the observed color indices of OB supergiants, in order to distinguish between interstellar and circumstellar extinction contributions. Methods. We first tested the influence of the wind on the UBV band fluxes of a model O supergiant star with artificial winds of different β values and a fixed interstellar extinction value. From the UBV magnitudes of these systems, the apparent interstellar extinction was then derived by calculating the values of E(B - V), from the (B - V) as well as from the (U - B) color index. Then we turned to a sample of galactic early-type B supergiants for which the stellar and wind parameters are known. All except one of these stars have β values higher than 1.0, which makes this set the most suitable one for our investigation. We calculated each star's wind contribution to the BV band fluxes. The observed magnitudes were corrected for the wind contributions, and the interstellar extinctions were derived and compared with those derived purely from the (B - V) color index. Results. From our model supergiant, we find that with increasing β the wind starts to influence the observable color indices. The wavelength dependence of the wind contribution is thereby different from that of the interstellar extinction contribution. Thus, the interstellar extinction values derived from the two color indices of our reddened star plus wind systems disagree. This effect is stronger for higher β. In addition, E(B ― V) derived from the (B ― V) color index always overestimates the real interstellar extinction. This trend is also found for the investigated B supergiant sample. Consequently, the luminosities of these stars are systematically overestimated. Our wind model always computes lower limits to the real wind contributions. This means that the real interstellar extinction values, hence the stellar luminosities of the studied B supergiant sample, might well be lower.

Methane, Ammonia, and Temperature Measurements of the Jovian Planets and Titan from CCD–Spectrophotometry

Full-disk albedo spectra of the jovian planets and Titan were derived from observations at the European Southern Observatory in July 1995. The spectra extend from 300 to 1050 nm wavelength. The spectral resolution is 0.4 nm between 520 and 995 nm, and 1 nm elsewhere. The accuracy of the albedo calibration is 4%. UBV magnitudes were also determined. Raman scattering was quantified for each planet. Methane and ammonia bands are shown at 0.4 nm spectral resolution, including a new band at 930 nm wavelength which is probably due to ammonia. Maps of the variation of these absorptions across the disks of Jupiter and Saturn are displayed. Saturn's spectrum is undisturbed by light from its rings due to the edge-on geometry during the observations. The albedo of Uranus near 1 μm wavelength has dropped almost 10% between 1993 and 1995, while there has been no change in the ultraviolet. The signature of light from Titan's surface yielded a path length of 4 km-am of methane in Titan's atmosphere. The temperature dependence of the width of the 890-nm methane band was used to measure temperature variations at three altitude levels, resulting in the first temperature maps of Jupiter and Saturn based on reflected sunlight. Jupiter displays a banded temperature structure with some discrete features of a few Kelvin amplitude. Saturn's north–south temperature asymmetry has reversed since the Voyager observations.

NEW MASSIVE STAR CLUSTER CANDIDATES IN M33

The central region of M33 is studied with aim new massive cluster candidates to be distinguished. This region has not been included in details in previous searches. From a collection of photographic plates, obtained under excellent seeing conditions at the Bulgarian National Observatory, using morphologic and photometric criteria, we have selected 26 new star cluster candidates, both young clusters and old globulars. Their coordinates and photographic UBV magnitudes are presented.

THE HOT STARS IN SYMBIOTIC SYSTEMS

ABSTRACT Symbiotic stars are interacting binaries, consisting of a late giant and a very hot companion, whose radiation ionizes the wind from the cool star. They strike the observers by their complex spectra and variability. A small subgroup, the symbiotic novae, undergo outbursts with an amplitude of several magnitudes and a duration of several decades. The ionizing binary component is usually too hot to be observed in the optical light. It emits mainly EUV photons, and in spectral regions better accessible to observers, nebula and cool star are much brighter than the hot star. Direct observations of hot components have therefore been restricted to special cases. Consequently, our knowledge about the hot components was poor. This thesis presents indirect methods allowing to extract crucial information on the ionizing star from the spectrum of the ionized nebula. Fundamental characteristics such as temperature, radius, and outburst energy are determined. They characterize the nature of the hot star, its outbursts, and the evolutionary status of the system. The IUE archive proved best suited as observational base. It contains thousands of far UV spectra of symbiotic stars. The UV continuum and the He II lambda-1640 recombination line turned out to be particularly sensitive to the hot star's parameters. For one object ROSAT observations of photospheric X-ray emission exist. They confirm the results obtained from IUE spectra. Unfortunately, only a subset of the symbiotics are bright enough to be observable in the UV, and moreover, the outburst of most symbiotic novae started long before the advent of space observatories. Possibilities to use optical spectroscopy are explored for these cases. T* can be derived from the observed ionization stages, and L* can be estimated from UBV magnitudes. The main result is displayed in Figure 1. Typically, the hot component of a symbiotic system has a radius ~0.1~R⊙, a surface temperature ~100,000~K, and a luminosity ~1000~L⊙. They occupy the same portion of the HR diagram as nova remnants and central stars of planetary nebulae. Like these, they seem to be basically white dwarfs with a hot atmosphere. They have not yet cooled or have been re-heated due to accretion of matter from the red giant. In particular, the results for the outbursts of symbiotic novae confirm the commonly adopted scenario of a thermo-nuclear event in an accreted layer on the surface of a white dwarf, largely analogous to a classical nova outburst. Unlike in classical novae, the cool component remains outside the outburst event, and the accreted matter slowly burns out over decades. While classical novae are hard to investigate when fading, the evolution of symbiotic novae can be tracked with the help of the subsisting nebular emission from the ionized part of the red giant's wind. The evolutionary paths roughly follow the theoretical models for novae. During the outburst of a symbiotic nova an energy around ~1047~erg is released, i.e. ~10-5 M⊙ of hydrogen is burnt. Besides supernovae, the outburst of symbiotic novae are the most energetic stellar events. The thesis is written in German.

The OB association LH 58 in the Large Magellanic Cloud

view Abstract Citations (39) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The OB Association LH 58 in the Large Magellanic Cloud Garmany, Catharine D. ; Massey, Philip ; Parker, Joel Wm. Abstract We present CCD photometry and spectroscopy for stars in Lucke-Hodge 58, an isolated OB association in the Large Magellanic Cloud (LMC) northwest of 30 Doradus. The photometric catalog contains 839 stars with UBV magnitudes complete to V~19. We have obtained spectra and classified 35 stars; combined with previous published spectral types, we find 22 O- type stars. The earliest type is O3-4 V and there are three WR stars in the association. The slope of the initial mass function, {GAMMA} = - 1.7 +/- 0.3, is in good agreement with other LMC associations. The presence of several evolved supergiants with masses about 15-25 M_sun_ suggests that some star formation took place as early as 10 million years ago, but the majority of stars formed coevally within the past few million years. Publication: The Astronomical Journal Pub Date: October 1994 DOI: 10.1086/117151 Bibcode: 1994AJ....108.1256G Keywords: Astronomical Catalogs; Astronomical Photography; Astronomical Spectroscopy; B Stars; Magellanic Clouds; O Stars; Star Formation; Stellar Mass; Stellar Spectra; Stellar Spectrophotometry; Supergiant Stars; Ubv Spectra; Wolf-Rayet Stars; Charge Coupled Devices; Color-Color Diagram; H Alpha Line; Hertzsprung-Russell Diagram; Stellar Luminosity; Astronomy; HII REGIONS; ISM: INDIVIDUAL OBJECTS: LH 58 full text sources ADS | data products SIMBAD (854) NED (1) CDS (1)

Sternberg WBVR photometric survey of bright stars

The paradox of situation in photoelectric multicolor photometry lies in the fact that there is not enough accurate and reliable photometric data in spite of large amount of these observations. Not all a stars included in Bright Stars Catalogue have UBV magnitudes.

Precision photometry of young stellar groups towards the outer Galactic disk and the Galactic rotation curve

view Abstract Citations (44) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Precision Photometry of Young Stellar Groups Towards the Outer Galactic Disk and the Galactic Rotation Curve Turbide, Luc ; Moffat, Anthony F. J. Abstract We have used a CCD to obtain stellar UBV magnitudes to V = 18 towards eight distant, young stellar groups in the third Galactic quadrant where interstellar extinction is low (l = 210 deg-242 deg). Comparison with theoretical isochrones yields ages and distances of significantly improved precision compared to previous studies based on photoelectric diaphragm photometry. One of the groups (in the faint H II region S 289) is located twice as far from the Galactic center as the sun and is likely located near the outer limit of active star formation in the Galactic disk. Together with published radial velocities and allowing for a metallicity gradient, the new distances harden the evidence for a flat Galactic rotation curve out to R about 16 kpc. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116558 Bibcode: 1993AJ....105.1831T Keywords: Astronomical Photometry; Charge Coupled Devices; Color-Magnitude Diagram; Galactic Rotation; Radial Velocity; Stellar Magnitude; Faint Objects; Interstellar Extinction; Astronomy; GALAXY: STELLAR CONTENT; GALAXY: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (39)

OPTICAL OBSERVATIONS OF ADS 9193

ABSTRACT ADS 9193 was first cataloged as a visual binary by Herschel (1831), who reported a position angle of 165 deg and a separation of 5 arcsec for the system. Additional measurements up through 1966 have revealed little substantive change in these parameters. Optical spectra and UBV magnitudes obtained for both components of ADS 9193, as well as direct CCD image of the field containing these stars, confirm the previous findings for the astrometric characteristics of ADS 9193, and establish the spectral types of components A and B as M6/7 and F6, respectively. Although the probability that ADS 9193 is an optical double is low, the observed V magnitude difference is only half what would be expected if the stars are at a common distance of approximately 200 pc, assuming the primary is a giant and its companion is on the main sequence.

A catalogue of flare stars in the Cygnus region

A catalogue of known flare stars in the region of the emission nebulae NGC 7000 - IC 5068-70 and IC 1318 a,b,c in Cygnus is presented. The UBV magnitudes and spectral types, as far as available, for 96 flare stars and their 144 flares were collected. Patrol observations from the Asiago, Byurakan, Konkoly, Rozhen and Tonantzintla observatories, covering a total of 1500 hours effective observing time were used.

Photometric variability in chromospherically active stars. III - The binary stars

view Abstract Citations (130) References (155) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Variability in Chromospherically Active Stars. III. The Binary Stars Strassmeier, Klaus G. ; Hall, Douglas S. ; Boyd, Louis J. ; Genet, Russell M. Abstract Differential UBV photometry of 49 late-type chromospherically active binary stars has been obtained. A total of 12,353 differential UBV magnitudes have been acquired and are used to determine seasonal photometric periods, amplitudes, mean brightnesses, maximum spot amplitudes, 'unspotted' differential magnitudes, and times of minimum light. Standard Fourier techniques are used to investigate the cause of the light variability. Eight stars are found which exhibit light variations due not to spot activity but rather to ellipticity and/or reflection effect. Others show combinations of all three effects. Some of the systems also show substantial differences between their rotational and orbital period. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1989 DOI: 10.1086/191310 Bibcode: 1989ApJS...69..141S Keywords: Astronomical Photometry; Binary Stars; Chromosphere; Stellar Activity; Ubv Spectra; Astronomical Catalogs; Fourier Analysis; Light Curve; Stellar Orbits; Stellar Rotation; Variability; Astronomy; PHOTOMETRY; STARS: BINARIES; STARS: CHROMOSPHERES; STARS: VARIABLES full text sources ADS | data products SIMBAD (98) Related Materials (2) Part 1: 1988ApJS...67..439S Part 2: 1988ApJS...67..453S

UBVRI field comparison stars for selected active quasars and BL Lacertae objects

UBV (Johnson) and RI (Cousins) magnitudes of field comparison stars for several active quasars and BL Lacertae objects are presented. The comparison stars can be used for photoelectric and CCD monitoring of the variability in brightness and optical-continuum spectral index of these BL Lacs and QSOs. 21 references.

A UBV PHOTOMETRIC STUDY OF THE OPEN CLUSTER NGC 654.

ABSTRACT Photographic UBV magnitudes and colors are presented for 83 stars in the region of the young open cluster NGC 654, which Stone (1977) determined to have nonzero membership probabilities. It is noted that one-third of these stars lie outside the cluster nuclear region, indicating the presence of a stellar corona. Further, the coronal stars can be used to investigate the known variable reddening in a cluster region much larger than considered in previous photometric studies. It is found that over the extended region, the reddening varies from E(B-V) = 0.77 to 1.13 magnitudes with several stars having larger reddenings, and a variable-extinction analysis gives an averaged absorption ratio of R = 2.9 + or - 0.6 (s.e.) which is in good agreement with an earlier study by Turner (1976). In addition, attention is given to the cluster H-R diagram, a study of the nuclear and coronal cluster regions, and a comparison of the cluster luminosity function with the Initial Luminosity Function of Sandage (1957).

Plans for A New Edition of the Bright Star Catalogue

Almost any star catalogue becomes obsolescent as soon as it comes off the press. It is now twelve years since the third edition of the Yale Bright Star Catalogue was published in 1964. In the intervening years numerous important new results have appeared, notably the Jaschek et al Catalogue of MK Spectral Classes, the Lick Double Star Catalogue, the U.S. Naval Observatory Catalogue of UBV Magnitudes, the Abt and Biggs Bibliography of Radial Velocities, the Third Edition and three Supplements of the General Catalogue of Variahle Stars, the SAO Catalogue with proper motions reduced to the FK4 system, several new lists of spectroscopic binaries, and a great many shorter compilations. Consequently well in excess of 20,000 entries in the third edition of the Bright Star Catalogue need up-dating.

SOME CHARACTERISTICS OF THE YOUNG OPEN CLUSTER TRUMPLER 37.

ABSTRACT New MK classifications (51 stars) and UBV magnitudes (37 stars) are presented for stars in the region of the cluster Trumpler 37, which is the nucleus of the association I Cephei (Cep OB 2). These are com bined with additional UBV magnitudes from Simonson (1968) and compared with the H-R diagram of upper Scorpius to derive a distance modulus of . The relationship of the supergiant Cep to the rest of the association is discussed and an absolute magnitude of -7.7 is derived if it is assumed to be a member. Key words: UBV photometry - MK spectral classification - clusters - associations