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1.
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).  相似文献   

2.
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 16d and amplitude of 0 . m 14 have been detected in theV-band.  相似文献   

3.
A Fourier analysis programme was applied on observational data taken in Stephanion Observatory, Greece, for flare star AD Leo. The purpose of this task is to try to register a short period variation in Johnson'sB-band in the star's brightness at quiet-state to confirm a result obtained by Pettersen (1980) inV-band of the flare star EV Lac. A negative result has been obtained.  相似文献   

4.
V934 Her is a detached system, consisting of a cool giant and a neutron star. The neutron star accretes matter fromthe stellarwind of the giant.Multicolor photoelectric observationsmade in 1997–2011 revealed a 415-day period, close to that, discovered spectroscopically from radial velocities. This period is considered to be the orbital period of orbital motion of the neutron star around the red giant. The wave with this period in the U-band has the largest amplitude 0m.12. We also detected multiperiodic pulsations of the red giant. The light curve in the V -band is dominated by a pulsation wave with the period of 28.82 days and the amplitude of 0m.10.  相似文献   

5.
Results of cooperative observations of the flare star EV Lac in September 1993 are presented. One of the about 30 optical flares detected was powerful enough to permit a quantitative analysis of its intrinsic radiation with the colour-colour technique. Sinusoidal brightness variations due to spottedness of the stellar surface was found to have an amplitude V = 0.m0.24. Behaviour of the K band stellar brightness during strong and weak U band flares are considered. The upper limits of very fast optical brightness variations were estimated during both a moderate flare and quiet state of the star. No decametric bursts were observed during the campaign that could be certainly attributed to flare activity.  相似文献   

6.
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 18m1 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.  相似文献   

7.
We present new results of our UBV photometry for HD 179821=V1427 Aql, an F supergiant with an infrared excess, from 2000 to 2008. The semiregular low-amplitude (ΔV = 0. m 05−0. m 20) photometric variability of the star with a cycle period from 130 to 200 days is caused by pulsations, along with the instability of a variable stellar wind. V1427 Aql also exhibits a long-term trend in the brightness and colors that is probably attributable to a change in the stellar temperature as a result of mass loss episodes, which cause variations in the continuum formation level. We present the results of our JHKLM photometry for V1427 Aql in 1992–2008. We trace the trend in the near-infrared brightness, which agrees with the long-term variability in the V band. Based on broadband photometry, we have determined the color excess for V1427 Aql: E(B−V) = 0.7. Based on low-resolution spectroscopy, we have estimated the stellar temperature and revealed variability of the Hα line caused by a change in the contribution from the emission component. The hypotheses of whether the star belongs to post-AGB objects or to massive yellow hypergiants are discussed.  相似文献   

8.
We present our long-term photometric and spectroscopic observations of a high-latitude B supergiant with an infrared excess—the protoplanetary nebula IRAS 18062+2410. OurU BV observations in 2000–2006 have confirmed the rapid irregular photometric variability of the star with a maximum amplitude as high as 0 . m 4 in V that we found previously. The B—V and U—B color indices vary with amplitudes as high as 0 . m 10 and 0 . m 25, respectively, and show no clear correlation with the brightness. Our V-band CCD observations on 11 nights in 2006 have revealed brightness trends during the night. The variability of IRAS18062+2410 is similar in pattern to the light variations in other hot post-AGB objects and some of the nuclei of young planetary nebulae. We assume that pulsations and a variable stellar wind can be responsible for the variability of these stars. In addition to the rapid variability, our 12-year-long observations have revealed a systematic decline in the mean brightness of IRAS 18062+2410. This may be related to a rise in the temperature of the star at constant luminosity as a result of its evolution. Low-resolution spectroscopic observations have shown a systematic increase in the equivalent widths of the Hα, Hβ, [NII]λ6584 Å, OI λ8446 Å, and [OII] λ7320–7330 Å emission lines. The changes in the star’s emission line spectrum are probably caused by an increase in the degree of ionization of the gas shell due to a rise in the temperature of the ionizing star. Our photometric and spectroscopic observations of IRAS 18062+2410 confirm the previously made assumptions that the star evolves very rapidly to the region of planetary nebulae.  相似文献   

9.
In searchs for flare stars in the vicinity of the Pleiades cluster, three flares were detected in 1970,1972, and 1977 in a star with the coordinates α 1950 = 3 h 48 m ·9, δ l950 = 25‡15’.8. The star’s brightness at a minimum is >21 m ·5. The star was tentatively assigned to the U Gem type. To confirm this assumption, we examined photographic plates for the period of 1947–1987. As a result, we found 12 more flares. The average recurrence time based on the 1963–1977 observations is about 330 days, and the maximum flare amplitude is >6 m .Narrow superflares and steady-state flares lasting over 40 days have been observed in the star. The results show that this is a dwarf nova of the UGSU subtype. Translated from Astrofizika, Vol. 42, No. 1, pp. 47–52, January–March, 1999.  相似文献   

10.
We present B and V light curves of a large stellar flare obtained with the Wide Field Camera at the Isaac Newton 2.5‐m telescope (La Palma). The source object is a faint (mV = 21.38) foreground star in the field of the Andromeda galaxy, with its most probable spectral type being dM4. We provide an estimate of the total flare energy in the optical range and find it to be of the order of 1035 erg. The cooling phase of the large flare shows three additional weak flare‐like events, which we interpret as results of a triggering mechanism also observed on the Sun during large coronal mass ejections. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
We have performed TreeSPH simulations of galaxy formation in a standard ΛCDM cosmology, including effects of star formation, energetic stellar feedback processes and a meta-galactic UV field, and obtain a mix of disk, lenticular and elliptical galaxies. The disk galaxies are deficient in angular momentum by only about a factor of two compared to observed disk galaxies. The stellar disks have approximately exponential surface density profiles, and those of the bulges range from exponential to r 1/4, as observed. The bulge-to-disk ratios of the disk galaxies are consistent with observations and likewise are their integrated B-V colours, which have been calculated using stellar population synthesis techniques. Furthermore, we can match the observed I-band Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk galaxies is (M/L I) ≃ 0.6–0.7. The ellipticals and lenticulars have approximately r 1/4 stellar surface density profiles, are dominated by non-disklike kinematics and flattened due to non-isotropic stellar velocity distributions, again consistent with observations. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

12.
Series of photometric and colorimetric observations of the Main-Belt asteroid 423 Diotima during its five oppositions were obtained at the Crimean Astrophysical Observatory. It was concluded, based on the results of a frequency analysis of the V-band photometry obtained in 1990, that the asteroid is a binary system: the rotation period of the primary component is equal to 4. h56, and the period of rotation and the orbital period of the satellite are equal to 14. h90. An analysis of simultaneous BV and BVR observations made in 1993 and 1998–1999 yielded a rotation period of 4. h54 ± 0. h01 for the primary component. An analysis of the sets of V-band observations of the asteroid made from 1982 through 2000 allowed us to find the period of forced precession, which was equal to 113d (or 226d). It was suggested that the axis of the primary component of the binary asteroid precesses and the large amplitude of brightness variations (about 1 m ) is due to its lenticular shape.  相似文献   

13.
The photoelectricV observations of the Scuti star 59 Aur have been analysed using the techniques of periodogram analysis and least-squares solutions. The fundamental mode is found to be more prominent than the first overtone in the pulsation of 59 Aur. The period ratio of the first overtone to the fundamental (i.e.,P 1/P 0=0.748) indicates that the star pulsates in the radial mode. The absolute magnitude, effective temperature and mass of the star are derived to be 1 . m 22, 7300 K and 2.0M , respectively. No variations exceeding±0 . m 01 about the mean values ofB-V andU-B colours have been found during a pulsation cycle.  相似文献   

14.
The results of photometry and polarimetry of the R Coronae Borealis type stars and other interesting objects are given. The observation of the former objects are obtained at the light maximum or at a brightness lower by 2-3 mag. The polarization of R CrB stars at light maximum has interstellar origin. The absolute magnitude of V 854 Cen is estimated to Msvw = −3m, and for Y Mus it is Mv > −3m.7. ρ Cas has a variable polarization and is probably a giant (Mv ≅ 0m) rather than a supergiant. Many early stars in its surroundings are photometrically and polarimetrically variable. The protoplanetary star BD −0°3679 has a polarization with the Rayleigh component.  相似文献   

15.
Spot photometry in theUBV was obtained for the flare star BY Dra during 1985-1991 at the Bulgarian National Astronomical Observatory. Light curves are presented for 1986, 1987, 1988, and 1991. There are significant variations of the amplitudes of the light curves implying changes of the spot distribution. The phases of the light minima are variable, indicating possible latitudinal migration of the spot and differential rotation. Rough estimate of the corresponding latitudinal shear is in the range 3 × 10–11 –5 × 10–10 rad s–1 deg–1. The photometric behaviour of BY Dra since 1960 shows no compeling evidence for existence of stellar cycles. This is in contradiction with previous studies. During 1985-1991 a total of 38.47 hours of monitoring in theU-filter were obtained. Analysis of the flare activity of BY Dra shows no significant changes from previous studies.  相似文献   

16.
UX Vir has been classified as an RRab star with the period of P =0.d51286 on the basis of new V(RI) C CCD photometry. A new variable star has also been discovered in the neighbourhood of UX Vir, which is most probably a flare star. The positions, reddening and distances have also been derived. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
The periodogram analysis of theV observations of the Scuti star HR 1225 has been carried out. Two frequencies of 6.415 cd (P 0=0 . d 1558) and 8.418 cd (P 1=0 . d 1188) have been determined. The period ratio ofP 1/P 0=0.762 indicates radial pulsation. The absolute magnitude, effective temperature and mass of the star are derived to be 1 . m 05, 7600 K and 1.9M , respectively.  相似文献   

18.
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.  相似文献   

19.
DifferentialUBV observations, carried out in 1990 observing season, of a small amplitude (0 . m 15 inV andB) W UMa system LS Del = HD 199497 are presented. Wavelength-dependent light variations from cycle to cycle indicate that the system is in a very active phase, probably due to magnetic flare activity or mass transfer in the system. An analysis of the minima times indicate a probable secular increase of the photometric period which requires a mass transfer from less massive to more massive component. If this is true then the reverse-algol model by Liuet al. (1988) for this system would not be valid.  相似文献   

20.
We present differential Hα and Hβ photometry of the very bright RS CVn‐binary α Aurigae (Capella)obtained with theVienna automatic photoelectric telescope in the years 1996 through 2000. Low‐level photometric variations of up to 0m.04 are detected in Hα. A multifrequency analysis suggests two real periods of 106 ± 3 days and 8.64 ± 0.09 days, that we interpret to be the rotation periods of the cool and the hot component of the Capella binary, respectively. These periods confirm that the hotter component of Capella rotates asynchronously, while the cooler component appears to be synchronized with the binary motion. The combined Hα data possibly contains an additional period of 80.4 days that we, however, believe is either spurious and was introduced due to seasonal amplitude variations or stems from a time‐variable circumbinary mass flow. The rotational periods result in stellar radii of 14.3 ± 4.6 R⊙ and 8.5 ± 0.5 R⊙ for the cool and hot component, respectively, and are in good agreement with previously published radii based on radiometric and interferometric techniques. The long‐period eclipsing binary Aurigae served as our check star, and we detected complex light variations outside of eclipse of up to 0m.15 in H α and 0m.20 in Hβ. Our frequency analysis suggests the existence of at least three significant periods of 132, 89, and 73 days. One of our comparison stars (HD 33167, F5V) was discovered to be a very‐low amplitude variable with a period of 2.6360 ± 0.0055 days.  相似文献   

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