The distribution of interstellar extinction near the sun

Photometric data inuvbyß system from 3713 stars is used to map the distribution of colour excesses up to 500 parsec from the Sun, producing diagrams for a series of layers aligned with the galactic plane. Individual clouds are detected, with a mean diameter of 6 parsecs, while cloud complexes have a mean diameter of 100 pc. From the maps it seems that the interstellar medium near the Sun presents regions of non-negligible extinction, while the Sun itself is enbedded in a diffuse cloud, or slightly off its border. The large scatter in the distribution ofE(b-) is confirmed, with a mean extinction ofA _v=0 _. ^m 38 up to 500 pc.     

NSV 01450: a New Bright Classical Cepheid in the Milky Way Field

Photometric data extracted from more than 5000 CCD observations of theMilky Way field star NSV 01450, with galactic co-ordinates l =145^°.9and b=4^° .9, show that this object is a bright classical Cepheid witha period of 12.639 ± 0.020 days and an average V magnitude of 11.045± 0.016. The computed colour excess is E(B-V)= 0.553± 0.056, yielding a distance modulus m _V -M_V of 15.537 ± 0.212.In addition, it was found that the star GSC 3730_0797 in the field ofNSV 01450 is also variable.     

Short-term variations of some UV-ceti type flare stars

Sinusoidal variations in bothV - andB-bands were detected in some flare stars of the UV Ceti type outside of flares. This detection has confirmed the light variation detection in Johnson'sV -band in EV Lac at quiet-state luminosity by Pettersen (1980) with a cyclic period equals about 4 _. ^d 378 and an amplitude of about 0 _. ^m 07. An interpretation of these short cyclic periods is that they are due to intensity modulations from a photospheric spot group as a result of stellar equatorial rotations. A short period of 14 days with an amplitude of 0 _. ^m 099 was detected inB-band in AD Leo. For the two flare stars, BD+55° 1823 and DO Cep in bothV- andB-bands, cyclic periods of more than 3 days and less than 17 days with amplitudes more than 0 _. ^m 090 and less than 0 _. ^m 250 have been registered. A significant contribution has been found in the flare star EV Lac in bothV- andB-bands at its quiescent-state luminosity where the detected cyclic periods are agreed with that which was detected by Pettersen (1980) in the same flare star in Johnson'sV-band, about 4 days. Furthermore, we found the same cyclic period in the colour index,B - V (about 4 days) which strengthens starspot phenomenon. This colour index period could not be detected by Pettersen (1980).     

Photoelectric observations of the flare star BD + 55° 1823

A light variation in Johnson'sV-band of flare star EV Lac has been registered by Pettersen (1980). The cycle length was 4 _. ^d 378 with amplitude about 0 _. ^m 07. A Fourier analysis programme has been applied on our measured data of the flare star BD+55°1823 in Johnson'sV andB bands. A period of 16^d and amplitude of 0 _. ^m 14 have been detected in theV-band.     

Photometry of the galactic cluster NGC 2169

The results of photoelectricU, B, V photometry of the galactic cluster NGC 2169 are presented. The colour excessE(B-V) is 0^m.18. The distance modulus to the cluster and its age are respectively estimated at 9^m.6 and 0.9×10⁷ yr. Star No. 10 is found to be variable.     

Analysis of Cassini/CIRS limb spectra of Titan acquired during the nominal mission II: Aerosol extinction profiles in the 600–1420 cm spectral range

We have analyzed the continuum emission of limb spectra acquired by the Cassini/CIRS infrared spectrometer in order to derive information on haze extinction in the 3–0.02 mbar range (∼150–350 km). We focused on the 600–1420 cm⁻¹ spectral range and studied nine different limb observations acquired during the Cassini nominal mission at 55°S, 20°S, 5°N, 30°N, 40°N, 45°N, 55°N, 70°N and 80°N. By means of an inversion algorithm solving the radiative transfer equation, we derived the vertical profiles of haze extinction coefficients from 17 spectral ranges of 20-cm⁻¹ wide at each of the nine latitudes. At a given latitude, all extinction vertical profiles retrieved from various spectral intervals between 600 and 1120 cm⁻¹ display similar vertical slopes implying similar spectral characteristics of the material at all altitudes. We calculated a mean vertical extinction profile for each latitude and derived the ratio of the haze scale height (H_haze) to the pressure scale height (H_gas) as a function of altitude. We inferred H_haze/H_gas values varying from 0.8 to 2.4. The aerosol scale height varies with altitude and also with latitude. Overall, the haze extinction does not show strong latitudinal variations but, at 1 mbar, an increase by a factor of 1.5 is observed at the north pole compared to high southern latitudes. The vertical optical depths at 0.5 and 1.7 mbar increase from 55°S to 5°N, remain constant between 5°N and 30°N and display little variation at higher latitudes, except the presence of a slight local maximum at 45°N. The spectral dependence of the haze vertical optical depth is uniform with latitude and displays three main spectral features centered at 630 cm⁻¹, 745 cm⁻¹ and 1390 cm⁻¹, the latter showing a wide tail extending down to ∼1000 cm⁻¹. From 600 to 750 cm⁻¹, the optical depth increases by a factor of 3 in contrast with the absorbance of laboratory tholins, which is generally constant. We derived the mass mixing ratio profiles of haze at the nine latitudes. Below the 0.4-mbar level all mass mixing ratio profiles increase with height. Above this pressure level, the profiles at 40°N, 45°N, 55°N, at the edge of the polar vortex, display a decrease-with-height whereas the other profiles increase. The global increase with height of the haze mass mixing ratio suggest a source at high altitudes and a sink at low altitudes. An enrichment of haze is observed at 0.1 mbar around the equator, which could be due to a more efficient photochemistry because of the strongest insolation there or an accumulation of haze due to a balance between sedimentation and upward vertical drag.     

Estimating the Luminosity Function of M51-Type Galaxies

A new sample of M51-type galaxies consisting of 46 systems is used to estimate the B-band luminosity function. The luminosity function for the primary components of the systems can be described by a Schechter function with the parameters _* = (1.4±0.3)×10^-5 Mpc^-3, = -1.3^+0.4 _-0.3, and M _* = -20.3^+0.2 _-0.1. The values of the latter two parameters are comparable to those for isolated galactic pairs. The resulting estimate of the average density of M51-type galaxies is (4±3)% of the average density of isolated pairs for luminosities in the range -22^m.0<M<-16^m.0     

Physical studies of asteroids IX: The light curve of the M asteroid 77 Frigga

The results of photoelectricUBV observations of asteroid 77 Frigga during the 1982 opposition are presented. From eight nights of observations at phase angles smaller than 2 _o ^. 8 a synodic period of 0 _d ^. 3755±0 _d ^. 0006 is derived. The light curve appears very symmetric with two maxima per period and an amplitude of 0 _m ^. 19. The primary maximum corresponds toV(0^o)=8 _m ^. 58, and the colour indices are:B–V = 0 _. ^m 738 ± 0 _. ^m 003 andU–B = 0 _. ^m 200 ± 0 _. ^m 002.     

Evidence for supernova-induced star formation in the monoceros OB2 association

The Monoceros ring, a circular optical nebulosity 3°.5 in diameter and centred at R.A.=6^h37^m, Dec.=6°30 (l ⁱⁱ =205°.5,b ⁱⁱ =0°.2) is in good structural agreement with radio observations. A neutral hydrogen shell is also accurately projected on the ring. These observations are consistent with the Monoceros ring being a supernova remnant 90–100 pc in diameter expanding at about 45 km s^–1 and having an age of the order of a million years. Bright Hii regions containing early-type stars (e.g., galactic cluster NGC 2244 in the Rosette nebula) and extremely young stars of the OB association Mon OB2 lie at the edges of the ring. The positional and temporal coincidence of the Mon OB2 association with a supernova remnant suggests that probably the star formation in this region is induced or speeded up by the passage of a supernova shock wave through the clumpy interstellar medium.     

Distribution of stars perpendicular to the plane of the galaxy

We present here rigorous analytical solutions for the Boltzmann-Poisson equation concerning the distribution of stars above the galactic plane. The number density of stars is considered to follow a behaviour n(m,0) ∼H(m - m₀)m^−x, wherem is the mass of a star andx an arbitrary exponent greater than 2 and also the velocity dispersion of the stars is assumed to behave as < v²(m)> ∼ m^−θ the exponent θ being arbitrary and positive. It is shown that an analytic expression can be found for the gravitational field K_z, in terms of confluent hypergeometric functions, the limiting trends being K_z∼z for z →0, while K_z → constant for z → infinity. We also study the behaviour of < |z(m)|²>,i.e. the dispersion of the distance from the galactic disc for the stars of massm. It is seen that the quantity < |z(m)|²>∼ m^t-θ, for m→ t, while it departs significantly from this harmonic oscillator behaviour for stars of lighter masses. It is suggested that observation of < |z(m)|²> can be used as a probe to findx and hence obtain information about the mass spectrum.     

UBV photometry at geographic latitude 69°22′ North

UBV measurements of the light of the night sky in the auroral zone during three seasons are presented. The mean brightness of the night sky in theV band is found to be equal one 18^m1 star (arc sec)^–2, with considerable variations. The observed meanB-V andU-B indicies are +0 _. ^m 7 and –1 _. ^m 6, respectively.Light curves of variable stars during strong auroral activities are also shown. On the basis of measurements we briefly discuss the possibility of accurate stellar photometry in the auroral region.     

Candidate red clump giants in the PPMX catalogue

This paper presents the RCGP catalogue of more than 0.5 million candidate red clump stars with the limiting magnitude K _s = 9.5 ^m . These stars are selected from the PPMX catalogue as the most probable red clump members by analyzing the color-reduced proper motion diagrams built from the proper motions given in PPMX and J, K _s -photometry given in the 2MASS catalogue. Reddening of the selected stars is used to find extinction in the K _s -band and to consider it in the further analysis. The two-dimensional galactic rotation model generalized by Ogorodnikov is used to investigate the tangential velocity field of the selected red clump members, most of which are thin disk stars located within 1.5 kpc from the sun. The values of kinematic parameters and solar components are determined as a function of stellar heights above the galactic equatorial plane and their heliocentric distances.     

Luminosity and colour distribution in the interacting system NGC 7770-71

Detailed surface photometry for the SB(s)a galaxy NGC 7771 has been carried out in the blue spectral band. Isophotes, luminosity profiles, and photometric parameters are obtained from photographs collected with the 74 inch telescope of Kottamia Observatory, Egypt. The total apparent magnitudem _T =13.08 with maximum dimensions 3.6±0.5×2.7±0.5 (at threshold µ _m = 27.38 mag s^–2). The absolute magnitude isM _T =–21.70 if the distance is =90.2 Mpc. The major axis is in position angle =69°.5±1° and the mean axis ratio of the outer regionsq=b/a=0.45 corresponds to an inclinationi=66°. The equivalent effective radiusr _e ^* =0.29 and the effective surface brightness µ _e = 22.30 mag s^–2.The equivalent luminosity distribution has been decomposed into two main components, anr ^1/4 spheroid and an exponential disk. The total apparent magnitudes of the spheroidal and disk components are 14.36 and 13.48, which correspond to contributions of 31 and 69% to the total blue luminosity, respectively.     

The scale and strength of the galactic magnetic field according to the pulsar data

In accordance with the data on the Faraday rotation, angular coordinates, and dispersion measurements and distances of 38 pulsars, the strengthB=2.1±1.1 G and directionl=99°±24°,b0° of the large-scale galactic magnetic field and the mean electron density in the galactic discN _e=0.03±0.01 cm^–3 are determined. A comparison with the results of a study of the measures of rotation of extragalactic radio sources enabled us to estimate the characteristic half-width of the distribution of the electron density on the Z-coordinate (h400 ps). The characteristic size of galactic magnetic field flucturations is shown to be =100–150 ps.     

Spectral classification of Be stars

In the course of observations of the LMC with the Glazar space telescope it was found that the star HD 269665 is unusually bright at 1640 A:m ₁₆₄₀ = 5 _. ^m ± 0 _. ^m 1,m ₁₆₄₀ –V = –6 _. ^m 2.     

Photometry of the contact binary system V471 Cas

UBV photoelectric observations of the W UMa-type binary V471 Cas were made from September to November 1984. Its colour indices were found to be(B-V)=0 _. ^m 771±0 _. ^m 02 and(U-B)=0 _. ^m 196±0 _. ^m 02. TheU, B, andV light curves of V471 Cas show some photometric fluctuations. We found that its orbital period is not 0.335998 days which was given by GCVS (1986), but 0.405356 days.Photometric orbital elements of V471 Cas were found using the Wilson-Devinney method. V471 Cas is a contact system, in which the overcontact factor is 0.19, its mass ratio of two components is 0.5947, and orbital minclination is in 83.29 degrees.     

Anisotropy in the Hubble relation for the brightest galaxies in clusters

The sky distribution of deviations from the mean Hubble relation for the brightest galaxies in clusters is non-random for the velocity range 4000<V _r<25 000 km s^–1. Deviations in visual magnitude are mainly positive in one large region of the sky and mainly negative in another region; the difference between the regions is 0.37±0.08 ^m and is independent of colour. Various explanations are discussed briefly, and galactic or intergalactic absorption may be excluded.     

Absolute Calibration of the PL-Relations for the Classical Cepheids Based on the HIPPARCOS Parallaxes and the Distances of the Magellanic Clouds

The zero points of the period-luminosity relations for the classical cepheids are calibrated based on the HIPPARCOS parallaxes of these stars. The calibrations are used to determine the distance moduli of the LMC and SMC: DM _LMC = 18^m.569 ± 0^m.117 and DM _SMC = 19^m.070 ± 0^m.119, respectively. It turns out that a calibration of the PL relations based on the distances of 25 FU classical cepheids in the galaxy by Gieren et al. yields a distance scale that is shorter by approximately 0^m.20 than the calibrations based on the HIPPARCOS parallaxes.     

Very short-term behaviour of the flare star EV Lac

Sinusoidal variations in Johnson'sB-band of the flare star EV Lac have been confirmed at its quiet state luminosity. The cycle lengths are more than one hour and less than two hours with amplitudes varying from 0 _. ^m 105 to 0 _. ^m 306. These registered cycles have agreed with cycles detected by Mavridis and Varvoglis (1990) and Mavridis (1990). In the same time, the cycles have confirmed the light variation detection in Johnson'sV-band in the same flare star by Pettersen (1980) with a cyclic period equals about 4 _. ^d 378 and an amplitude of about 0 _. ^m 07. Our net results confirm, to some extent, the presence of active region(s) as an origin of stellar flare phenomenon of UV Ceti type flare stars. We can cautiously say that the solar and stellar flare phenomenon have a similar origin.     

Light curve solutions for eclipsing binaries in NGC 188

We present light curve solutions for the W UMa-type eclipsing binaries EP, EQ, ER, ES, and V369 Cep in the old open cluster NGC 188. Using light curve solution parameters combined with reasonable mass estimates, we determine the distance modulusV-M _vof the cluster. Our aim is to examine if current uncertainties in the cluster's distance and age can be resolved. Three binaries yield distance moduli close to 10 _. ^m 80 (±0 _. ^m 08), two others give values around 11 _. ^m 40(±0 _. ^m 09). Depending on the amount of reddening, we find a weighted mean distance modulus for all five binaries between 11 _. ^m 01 and 11 _. ^m 05 (±0 _. ^m 06), which lends modest support for the lower distance (1.65 kpc) and older age (10 Gyr) of the cluster.Participants in the Research Experience for Undergraduates (REU) program at Florida International University, sponsored by the National Science Foundation.