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1.
We report simultaneous multicolour observations in 5 bands (UBVRI) of the flickering variability of the cataclysmic variable AE Aqr. Our aim is to estimate the parameters (colours, temperature, size) of the fireballs that produce the optical flares. The observed rise times of the optical flares are in the interval 220‐440 s. We estimate the dereddened colours of the fireballs as (U ‐B)0∼0.8‐1.4, (B ‐V)0∼0.03‐0.24, and (V ‐I)0∼0.26‐0.78. We find for the fireballs temperatures of 10000‐25000 K, masses of (7‐90)x1019 g, and sizes of (3‐7)x109 cm (using a distance of d = 86 pc). These values refer to the peak of the flares observed in the UBVRI bands. The data are available upon request from the authors (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
Lutz‐Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main‐sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson‐Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% (σπ/π ≤ 0.15). The calibration equations which provide the corrected absolute magnitude for optical and near‐infrared pass bands are valid for wide ranges of colours and absolute magnitudes: –0.18 < (B – V)0 < 0.91, –1.6 < MV < 5.5 and –0.15 < (J – H)0 < 0.50, –0.02 < (H – Ks)0 < 0.13, 0 < MJ < 4, respectively. The distances computed using the luminosity‐colours (LCs) relation with optical (BV) and near‐infrared (JHKs) observations were compared to the distances found from various other methods. The results show that new absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
Broadband colours are often used as metallicity proxies in the study of extragalactic globular clusters. A common concern is the effect of variations in horizontal branch (HB) morphology – the second‐parameter effect – on such colours. We have used UBVI, Washington, and DDO photometry for a compilation of over 80 Milky Way globular clusters to address this question. Our method is to fit linear relations between colour and [Fe/H], and study the correlations between the residuals about these fits and two quantitative measures of HB morphology. While there is a significant HB effect seen in U – B, for the commonly used colours B – V, V – I, and C – T1, the deviations from the baseline colour‐[Fe/H] relations are less strongly related to HB morphology. There may be weak signatures in B –V and C –T1, but these are at the limit of observational uncertainties. The results may favour the use of B –I in studies of extragalactic globular clusters, especially when its high [Fe/H]‐sensitivity is considered. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
New photoelectric UBV observations were obtained for the eclipsing binary TT Her at the Ankara University Observatory (AUO) and three new times of minima were calculated from these observations. The (O – C) diagram constructed for all available times of minima of TT Her exhibits a cyclic character superimposed on a quadratic variation. The quadratic character yields an orbital period decrease with a rate of dP /dt = –8.83 × 10–8 day yr–1 which can be attributed to the mass exchange/loss mechanism in the system. By assuming the presence of a gravitationally bound third body in the system, the analysis of the cyclic nature in the (O – C) diagram revealed a third body with a mass of 0.21M⊙ orbiting around the eclipsing pair. The possibility of magnetic activity cycle effect as a cause for the observed cyclic variation in the (O – C) diagram was also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
We present new photometric observations of 15 symbiotic stars covering their last orbital cycle(s) from 2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD photometry. Main results are: EG And brightened by ∼0.3 mag in U from 2003. A ∼0.5 mag deep primary minimum developed in the U light curve (LC) at the end of 2006. ZAnd continues its recent activity that began during the 2000 autumn. A new small outburst started in summer of 2004 with a peak U magnitude of ∼ 9.2. During the spring of 2006 the star entered a massive outburst. It reached its historical maximum at U ∼ 8.0 in 2006 July. AEAra erupted in 2006 February with Δmvis ∼ 1.2 mag. BF Cyg entered a new active stage in 2006 August. A brightness maximum (U ∼ 9.4) was measured during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June–December a ∼ 2 mag decline in all colours was measured. CI Cyg started a new active phase during 2006 May–June. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
We present the results of 10 years of photometric CCD observations of the intermediate polar V709 Cas obtained by using different instruments during 2003–2013. We detected a new variability with a period of Pnew = 0.d016449979(5) which seems to be real. The spin variability is not clearly seen in all our data, so we are unable to study any evolution of the white dwarf rotation. From the best night (in 2010) we obtained a spin period of Pspin = 311.s8(5). We analyzed the orbital variability using (O – C) analysis. We found no variations of the orbital period on a timescale of 10 years, but the linear fit to the (O – C) diagram shows that the value of the orbital period is Porb = 0.d2222123(6), which is close to the earlier published values. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
A catalogue of photoelectric stellar magnitudes and colours in the UBVR Johnson system in 47 sky areas with galaxies near the Main Galactic Meridian is presented. The catalogue includes 1141 stars within the V magnitude interval 4m.5–15m.5. The rms errors are ±0.014, ±0.026, ±0.012, ±0.016 mag for stellar magnitudes V and colours (U – B),(B – V),(V – R), respectively. The catalogue contains accurate equatorial coordinates (α, δ)1950.0, too.  相似文献   

8.
This paper is based on 2MASS photometry (J H Ks magnitudes) of 1172 Be stars. The observed mean intrinsic colours have been derived with aid of two‐colour diagrams for Be stars of luminosity classes Ie‐IIe, IIIe and IVe‐Ve. The obtained results are the first determinations of their intrinsic colours in the astronomical literature. The smoothed infrared colours are compared with those obtained for “normal” B stars. Several two‐colour diagrams and plots of observed and smoothed intrinsic colour versus spectral type of luminosity classes Ie‐IIe, IIIe and IVe‐Ve are presented. Generally the determined infrared intrinsic colours of Be stars (V – J)0, (V – H)0, and (V – Ks)o differ substantially from those of “normal” B stars. It is found that the intrinsic colours of B stars are generally bluer than Be stars of corresponding spectral type and luminosity class. The mean absolute visual magnitude Mv of 528 Be stars for luminosity classes Iae, Ibe‐Iabe, IIe, IIIe and IVe‐Ve is derived from HIPPARCOS parallaxes. The Mv calibration is compared with the existing ones. The Be stars are generally brighter than “normal” B stars of corresponding spectral types. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed. 31 W UMa stars, which have the most accurate parallaxes (σπ /π < 0.15) which are neither associated with a photometric tertiary nor with evidence of a visual companion, were selected for re‐calibrating the Period‐Luminosity‐Color (PLC) relation of W UMa stars. Using the Lutz‐Kelker (LK) bias corrected (most probable) parallaxes, periods (0.26 < P < 0.87, P in days), and colors (0.04 < (B – V)0 < 1.28) of the 31 selected W UMa, the PLC relation have been revised and re‐calibrated. The difference between the old (revised but not bias corrected) and the new (LK bias corrected) relations are almost negligible in predicting the distances of W UMa stars up to about 100 pc. But, it increases and may become intolerable as distances of stars increase. Additionally, using (J – H)0 and (H – Ks)0 colors from 2MASS (TwoMicron All Sky Survey) data, a PLC relation working with infrared data was derived. It can be used with infrared colors in the range –0.01 < (J – H)0 < 0.58, and –0.10 < (H – Ks)0 < 0.18. Despite of the fact that the 2MASS data refer to single epoch observations which are not guaranteed to be taken at maximum brightness of theWUMa stars, the established relation has been found surprisingly consistent and reliable in predicting LK corrected distances of W UMa stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
Solutions of the new standard V‐light curves for the EA type binary UV Leo are obtained using the PHOEBE code (0.31a version). Absolute parameters of the stellar components were then determined, enabling them to be positioned on the absolute magnitude‐color (l.e. MV vs. B – V) isochrones diagram, based on which the age of the system is estimated to be >4×109 yr. Also times of minima data (“O – C curve”) have been analyzed. Apart from an almost sinusoidal variation with a period of 29.63 yr, which modulates the orbital period, and was attributed to a third body orbiting around the system, other cyclic variation in the orbital period and also brightness, with time scales of 24.25 and 22.77 yr were found, respectively. We associate this with a magnetic activity cycle newly reported here for UV Leo (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
We present the analysis of 20 years of time‐series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B – V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9‐year time scale. We also find some evidence for brightness variability on a time scale longer than the 20‐year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.m154, which is ≈0.m2 brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B – V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip‐flop phenomenon. We estimate the differential rotation coefficient of the star as k = 0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45° (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
We present the first ever study of the bright star HD 1. The star was chosen arbitrarily just because of its outstanding Henry Draper number. Surprisingly, almost nothing is known about this bright 7.m4 star. Our observations were performed as part of the commissioning of the robotic telescope facility STELLA and its fiber‐fed high‐resolution optical echelle spectrograph SES in the years 2007–2010. We found long‐term radial velocity variations with a full amplitude of 9 km s–1 with an average velocity of –29.8 km s–1 and suggest the star to be a hitherto unknown single‐lined spectroscopic binary. A preliminary orbit with a period of 6.2 years (2279±69 days) and an eccentricity of 0.50±0.01 is given. Its rms uncertainty is just 73 m s–1. HD 1 appears to be a G9‐K0 giant of luminosity class IIIa with Teff = 4850±100 K, logg = 2.0±0.2, L ≈ 155 L⊙, a mass of 3.0±0.3 M⊙, a radius of 17.7 R⊙, and an age of ≈350 Myr. A relative abundance analysis led to a metallicity of [Fe/H] = –0.12 ± 0.09. The α ‐element silicon may indicate an overabundance of +0.13 though. The low strengths of some s‐process lines and a lower limit for the 12C/13C isotope ratio of ≥16 indicate that HD 1 is on the first ascend of the RGB. The absorption spectral lines appear rotationally broadened with a v sin i of 5.5±1.2 km s–1 but no chromospheric activity is evident. We also present photometric monitoring BV (RI)C data taken in parallel with STELLA. The star is likely a small‐amplitude (<10 mmag) photometric variable although no periodicity was found (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
This article discusses the interstellar extinction curve in the visible and the value of the ratio of absolute to selective extinction RV = AV/E (B – V). It is concluded that the visible extinction curve is likely to be linear in the visible and that indirect estimates of RV from tentative determinations of AV or from infrared and UV observations are questionable. There is currently no evidence of any variation of RV with direction. If RV is close to 3, as it has been inferred from mid‐infrared data, starlight in the visible is extinguished by a factor F /F0 = (2.5 e–2μm/λ)E (B –V). But if the visible wavelength range alone is considered, 4 appears as its most natural and probable value and F /F0 = e–2E (B –V)/λ (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
Photometric and spectroscopic characteristics of the WN5+O6 binary system, V444 Cyg, were studied. The Wilson‐Devinney (WD) analysis, using new BV observations carried out at the Ankara University Observatory, revealed the masses, radii, and temperatures of the components of the system as MWR = 10.64 M⊙, MO = 24.68 M⊙, RWR = 7.19 R⊙, RO = 6.85 R⊙, TWR = 31 000 K, and TO = 40000 K, respectively. It was found that both components had a full spherical geometry, whereas the circumstellar envelope of the WR component had an asymmetric structure. The O – C analysis of the system revealed a period lengthening of 0.139 ± 0.018 syr–1, implying a mass loss rate of (6.76 ± 0.39) ×10–6 M⊙ yr–1 for the WR component. Moreover, 106 IUE‐NEWSIPS spectra were obtained from NASA's IUE archive for line identification and determination of line profile variability with phase, wind velocities and variability in continuum fluxes. The integrated continuum flux level (between 1200–2000 Å) showed a mild and regular increase from orbital phase 0.00 up to 0.50 and then a decrease in the same way back to phase 0.00. This is evaluated as the O component making a constant and regular contribution to the system's UV light as the dominant source. The C IV line, originating in the circumstellar envelope, had the highest velocity while N IV line, originating in deeper layers of the envelope, had the lowest velocity. The average radial velocity calculated by using the C IV line (wind velocity) was found as 2326 km s–1 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
The variable star SU Equulei was classified as a close binary with an eclipse light curve previously categorized as WUMa type. The aim of this paper is a review of this old classification on the basis of new observations and a new determination of variable star ephemeris as well as the determination of SU Equ spectral type and distance. New photometric observations in different colours allow a precise determination of the period of variability and yield more accurate light curves allowing a re‐classification of the type of variability. We find the best period of variability to be half the old value. The shape of the light curve is inconsistent with an eclipse curve but consistent with an RR Lyrae type c classification. From the B, V, and R colours we deduce a new spectral classification. SU Equulei is an RRc Lyrae type variable of spectral class A8 at a distance of ≈12.4 kpc instead of a late‐type eclipsing binary (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
In this work, the analysis of the photoelectric light curve (LC) in the broad‐band filter (400–700 nm) for the UU And system was carried out using the PHOEBE program (vers. 0.31a). The absolute dimensions of the system are determined and its evolution is discussed. Moreover, the period changes of the system are studied using updated O – C data, which shows a cyclic change with a period of Pmod = 18 yr. This was attributed to a magnetic activity cycle operating in this system. In addition to the cyclic change, a long‐term secular variation due to mass transfer from the secondary to the primary component with a rate of 6.17×10–9 M⊙ yr–1 was also detected. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
《New Astronomy》2007,12(7):597-604
We investigate the effect on the U, B, V, RC and RJ magnitudes of the removal of emission lines from a spectrum. We determined Δm corrections from the ratio of fluxes with and without emission lines, transmitted from the object through a photometric filter. An exact and simplified approach for operative use was applied. The effect was demonstrated for classical symbiotic stars, symbiotic novae and the classical nova V1974 Cyg. It was found that about 20–30%, 30–40%, 10% and 26/20% of the observed flux in the U, B, V and RC/RJ filters, respectively, are radiated in the emission lines of the investigated classical symbiotic stars. The largest effect was found for symbiotic novae (RR Tel and V1016 Cyg) and the classical nova V1974 Cyg at 210 days (an average of 74%, 79%, 56% and 66/60%), because of their very strong emission line spectrum. In all cases, the line corrected flux points fit the theoretical continuum well. The difference between Δm corrections obtained by the accurate calculation and that given by our approximate formula is less than 10%. Deviations up to 30% can exist only in the U passband. Examples for practical applications are suggested.  相似文献   

18.
We have used two robotic telescopes to obtain time‐series high‐resolution optical echelle spectroscopy and VI and/or by photometry for a sample of 60 active stars, mostly binaries. Orbital solutions are presented for 26 double‐lined systems and for 19 single‐lined systems, seven of them for the first time but all of them with unprecedented phase coverage and accuracy. Eighteen systems turned out to be single stars. The total of 6609 R = 55000 échelle spectra are also used to systematically determine effective temperatures, gravities, metallicities, rotational velocities, lithium abundances and absolute Hα‐core fluxes as a function of time. The photometry is used to infer unspotted brightness, V – I and/or b – y colors, spot‐induced brightness amplitudes and precise rotation periods. An extra 22 radial‐velocity standard stars were monitored throughout the science observations and yield a new barycentric zero point for our STELLA/SES robotic system. Our data are complemented by literature data and are used to determine rotation‐temperature‐activity relations for active binary components. We also relate lithium abundance to rotation and surface temperature. We find that 74% of all known rapidly‐rotating active binary stars are synchronized and in circular orbits but 26% (61 systems) are rotating asynchronously of which half have Prot > Porb and e > 0. Because rotational synchronization is predicted to occur before orbital circularization active binaries should undergo an extra spin‐down besides tidal dissipation. We suspect this to be due to a magnetically channeled wind with its subsequent braking torque. We find a steep increase of rotation period with decreasing effective temperature for active stars, Prot α T–7eff, for both single and binaries, main sequence and evolved. For inactive, single giants with Prot > 100 d, the relation is much weaker, Prot α T‐1.12eff. Our data also indicate a period‐activity relation for Hα of the form RHα α P0.24rot for binaries and RHα α P‐0.14rot for singles. Its power‐law difference is possibly significant. Lithium abundances in our (field‐star) sample generally increase with effective temperature and are paralleled with an increase of the dispersion. The dispersion for binaries can be 1–2 orders of magnitude larger than for singles, peaking at an absolute spread of 3 orders of magnitude near Teff ≈ 5000 K. On average, binaries of comparable effective temperature appear to exhibit 0.25 dex less surface lithium than singles, as expected if the depletion mechanism is rotation dependent. We also find a trend of increased Li abundance with rotational period of form log n (Li) α –0.6 log Prot but again with a dispersion of as large as 3‐4 orders of magnitude (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
We present continuous and time‐resolved R = 55 000 optical échelle spectroscopy of ε Aurigae from 2006–2013. Data were taken with the STELLA Echelle Spectrograph of the robotic STELLA facility at the Observatorio del Teide in Tenerife. Contemporaneous photometry with the Automatic Photoelectric Telescopes at Fairborn Observatory in Arizona is presented for the years 1996–2013. Spectroscopic observations started three years prior to the photometric eclipse and are still ongoing. A total of 474 high‐resolution échelle spectra are analyzed and made available in this paper. We identify 368 absorption lines of which 161 lines show the characteristic sharp disk lines during eclipse. Another 207 spectral lines appeared nearly unaffected by the eclipse. From spectrum synthesis, we obtained the supergiant atmospheric parameters Teff = 7395 ± 70 K, log g ≈ 1, and [Fe/H] = +0.02 ± 0.2 with ξt = 9 km s–1, ζRT = 13 km s–1, and v sin i = 28 ± 3 km s–1. The residual average line broadening expressed in km s–1 varies with a period of 62.6 ± 0.7 d, in particular at egress and after the eclipse. Two‐dimensional line‐profile periodograms show several periods, the strongest with ≈110 d evident in optically thin lines as well as in the Balmer lines. Center‐of‐intensity weighted radial velocities of individual spectral lines also show the 110‐d period but, again, additional shorter and longer periods are evident and are different in the Balmer lines. The two main spectroscopic Hα periods, ≈ 116 d from the line core and ≈ 150 d from the center‐of‐intensity radial velocities, appear at 102 d and 139 d in the photometry. The Hβ and Johnson V I photometry on the other hand shows two well‐defined and phase‐coherent periods of 77 d and 132 d. We conclude that Hα is contaminated by changes in the circumstellar environment while the Hβ and V I photometry stems predominantly from the non radial pulsations of the F0 supergiant. We isolate the disk‐rotation profile from 61 absorption lines and found that low disk eccentricity generally relates to low disk rotational velocity (but not always) while high disk eccentricity always relates to high velocity. There is also the general trend that the disk‐absorption in spectral lines with higher excitation potential comes from disk regions with higher eccentricity and thus also with higher rotational velocity. The dependency on transition probability is more complex and shows a bi‐modal trend. The outskirts of the disk is distributed asymmetrically around the disk and appears to have been built up mostly in a tail along the orbit behind the secondary. Our data show that this tail continues to eclipse the F0 Iab primary star even two years after the end of the photometric eclipse. High‐resolution spectra were also taken of the other, bona‐fide, visual‐binary components of ε Aur (ADS 3605BCDE). Only the C‐component, a K3‐4‐giant, appears at the same distance than ε Aur but its radial velocity is in disagreement with a bound orbit. The other components are a nearby (≈ 7 pc) cool DA white dwarf, a G8 dwarf, and a B9 supergiant, and not related to ε Aur. The cool white dwarf shows strong DIB lines that suggest the existence of a debris disk around this star. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
A possible scenario for the evolution of the universe following the big bang at t > 10-5 sec is considered. The necessary conditions that must be present for the formation of stars and stellar systems to be possible are formulated. As a condition for the formation of stars we take kTs≤ GMsmp(3R), and for stellar systems HR ? (GM/R)1/2, where Ts is the temperature of the cosmic plasma, mp is the mass of a proton, Ms is the mass of a star, M is the mass of a stellar cluster, R is the radius of these celestial bodies, and H is the bubble parameter for the corresponding time. In accordance with these criteria, we assume that in the course of cosmological expansion, neutron stars should have been formed first (times 2.10-4 ? t ? 1 sec, densities 0.07 ? ρB? 2.104 g/cm3) and then, in chronological order, appeared white dwarfs (t ≈ 102 sec, ρB ? 5.10-3 g/cm3), ordinary stars (t ≈ 4.106 sec, ?B ≈ 10-11 g/cm3), galactic nuclei (t ≈ 3.1011 sec, ?B ≈ 5.10-19 g/cm3, globular clusters (t ≈ 1013 sec, ?B ≈ 4.10-21 g/cm3), and galaxies (t ≈ 1015 sec, ?B ≈ 10-24 g/cm3), where ?B is the average density of ordinary (baryon) matter in the universe. It is shown that a galactic nucleus is a stellar system in statistical equilibrium and consists mainly of neutron stars and white dwarfs. The formation of some pulsars (neutron stars with angular rotation rates 1 < Ω < 200 sec-1) may occur in a galactic nucleus. Observed pulsars should therefore contain some fraction of neutron stars from the nucleus of the Galaxy that were able to escape it over the relaxation time (the tail of the Maxwell distribution, with star velocities v > v0, where v0 is the velocity corresponding to the work function 2GMMs/R, M being the mass and R the radius of the Galaxy’s nucleus.  相似文献   

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