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1.
We derive astrophysical and structural parameters of the poorly studied open clusters NGC 6866, NGC 7062, and NGC 2360 based on filtered 2MASS (J, J ? H) diagrams, and stellar radial density profiles. The field star decontamination technique is utilised for selecting high-probability cluster members. The E(B ? V) reddening values of the three clusters derived from 2MASS JHKs agree with those inferred from UBV and uvby ? β photometries. We find that the core mass function slopes are flatter than the halo’s for the three clusters. The large core and cluster radii of NGC 6866 and NGC 2360 indicate an expanded core, which may suggest the presence of stellar mass black-holes. NGC 2360 is located in the third quadrant (? = 229°.80), where Giant Molecular Clouds are scarce that, together with its relatively large mass (～1800 m⊙), might explain its longevity (～1.8 Gyr) in the Galaxy.  相似文献   

2.
《New Astronomy》2007,12(2):117-123
Both V701 Sco and BH Cen are two early-type short-period overcontact systems (P = 0.d762 and P = 0.d792, respectively). V701 Sco is a member of the young galactic cluster NGC 6383, while BH Cen is a component of a younger galactic cluster IC 2944 where star formation is in process. They provide good opportunity to understand the formation and evolution of binary stars. In the present paper, orbital period changes of the two binaries are investigated. It is discovered that the orbital period of BH Cen shows a long-term increase with a rate of dP/dt = +1.70(±0.39) × 10−7 days/year while it undergoes a cyclic oscillation with a period of 44.6 years and an amplitude of A3 = 0.d0216. For V701 Sco, its O-C curve reveals a periodic change with a period of 41.2 years and amplitude of A3 = 0.d0158. The mass ratio of BH Cen is 0.84, but V701 Sco contains twin B1-1.5V type stars with a mass ratio of unit. The continuous period increase of BH Cen is caused by the mass transfer from the less massive component to the more massive one at a rate of dM2/dt = 3.5 × 10−6 days/year.The cyclic period changes of both systems can be plausibly explained as the results of light-travel time effects suggesting that they are triple systems. The astrophysical parameters of the unseen tertiary components in the two systems have been determined. We think that the invisible tertiary components in both binaries played an important role in the formations and evolutions of the overcontact configurations by bringing angular momentum out from the central systems. For BH Cen, this process created the initial short period and will support its evolution into an overcontact configuration via a Case A mass transfer within the life time of the extremely young cluster IC 2944. For V701 Sco, two identical zero-age main-sequence components in an overcontact configuration suggest that it may have been formed by fission, possibly by the fission of the third body. The fact that no long-term continuous period variations were found for V701 Sco may suggest that an overcontact binary with the mass ratio of unity can be in an equilibrium revealing that the original configuration of the binary was overcontact as is its present state. It has been reported that faint stars in the two extremely young clusters are relatively scare. From the present study, it is shown that faint stars in young clusters are usually formed as companions of OB stars (including binaries). It is very difficult to detect them because of their low luminosity when compared with the more luminous OB stars.  相似文献   

3.
Despite the continuing importance of ground-based parallax measurements, few active programs remain. Because new members of the solar neighborhood tend towards later spectral types, infrared parallax programs are particularly desirable. Therefore, the astrometric quality of the new infrared camera, FanCam, developed by the Virginia Astronomical Instrumentation Laboratory (VAIL) for the 31-in. (0.8 m) Tinsley reflector at Fan Mountain Observatory was assessed using 68 J-band exposures of an open cluster, NGC 2420, over a range of hour angles during 2005. Positions of 16 astrometric evaluation stars were measured and the repeatability of those positions was evaluated using the mean error in a single observation of unit weight. Overall, a precision of 1.3 ± 0.7 μm in x (RA) and 1.3 ± 0.8 μm in y (Dec) was attained, which corresponds to 0.04″ ± 0.02″ in each axis. Although greater precision is expected from CCDs in the visual and near-infrared, this instrument can achieve precision similar to that of the ESO NTT infrared parallax program. Therefore, measuring parallaxes in the infrared would be feasible using this equipment. If initiated, such a program could provide essential distances for brown dwarfs and very low mass stars that would contribute significantly to the solar neighborhood census.  相似文献   

4.
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5.
In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M⊙, and the semi-major axis of its orbit is 10.75 AU.  相似文献   

6.
We present new B- and V-band photometry of the W UMa-type binary system QX And, which is a member of the open cluster NGC 752. Revised orbital period and new ephemerides were given for the binary system based on the data of times of light minima. The result of a period analysis reveals that the system is undergoing a continuous orbital period increase during the past decades. The rate of period increasing turns out to be about 2.7 × 10?7 d yr?1. With the Wilson–Devinney code, a photometric solution is computed. It yields a contact configuration for the system with a filling factor of 0.361. Combining the results from the photometric solution along with that from the radial-velocity observations, we have determined the absolute parameters for the two components of the system. The masses, radii and luminosity of the primary and secondary stars are calculated as 1.43 ± 0.04 M⊙, 1.45 ± 0.09 R⊙, 2.87 ± 0.40 L⊙ and 0.44 ± 0.02 M⊙, 0.87 ± 0.05 R⊙, 0.99 ± 0.13 L⊙, respectively. The evolutionary status and physical nature of the contact binary system were discussed compared with the theoretical models.  相似文献   

7.
Ultraviolet spectra from the International Ultraviolet Explorer (IUE) and from the Hubble Space Telescope (HST) of the symbiotic novae AG Peg during the period 1978–1996 are analyzed. Some spectra showing the modulations of spectral lines at different times are presented. We determined the reddening from the 2200 Å feature, finding that E(B−V) = 0.10 ± 0.02. We studied N IV] at 1486 Å, C IV 1550 Å, and O III] at 1660 Å, produced in the fast wind from the hot white dwarf. The mean wind velocity of the three emission lines is 1300 km s−1 (FWHM). The mean wind mass loss rate is ∼6 × 10−7 M⊙ yr−1. The mean temperature is ∼6.5 × 105 K. The mean ultraviolet luminosity is ∼5 × 1033 erg s−1. The modulations of line fluxes in the emitting region at different times are attributed to the variations of density and temperature of the ejected matter as a result of variations in the rate of mass loss.  相似文献   

8.
We suggest that planets, brown dwarfs, and even low mass stars can be formed by fragmentation of protoplanetary disks around very massive stars (M ? 100 M⊙). We discuss how fragmentation conditions make the formation of very massive planetary systems around very massive stars favorable. Such planetary systems are likely to be composed of brown dwarfs and low mass stars of ～0.1–0.3 M⊙, at orbital separations of ～ few × 100–104 AU. In particular, scaling from solar-like stars suggests that hundreds of Mercury-like planets might orbit very massive stars at ～103 AU where conditions might favor liquid water. Such fragmentation objects can be excellent targets for the James Webb Space Telescope and other large telescopes working in the IR bands. We predict that deep observations of very massive stars would reveal these fragmentation objects, orbiting in the same orbital plane in cases where there are more than one object.  相似文献   

9.
We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 m telescope of IUCAA Girawali Observatory, India. The star was classified as a W UMa type binary of subtype-W by Samec et al. (1996). The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by Samec et al. (1996). A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature difference of ΔT = 141 ± 10 K between the components and an orbital inclination of i[°] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell effect is explained by the presence of a hot spot on the primary component.  相似文献   

10.
This paper presents new CCD Bessell BVRI light curves and photometric analysis of the Algol-type binary star TX Her. The CCD observations were carried out at Çanakkale Onsekiz Mart University Observatory in 2010. New BVRI light curves from this study and radial velocity curves from Popper (1970) were solved simultaneously using modern light and radial velocity curves synthesis methods. The general results show that TX Her is a well-detached eclipsing binary, however, both component stars fill at least half of their Roche lobes. A significant third light contribution to the total light of the system could not be determined. Using O–C residuals formed by the updated minima times, an orbital period study of the system was performed. It was confirmed that the tilted sinusoidal O–C variation corresponds to an apparent period variation caused by the light travel time effect due to an unseen third body. The following absolute parameters of the components were derived: M1 = 1.62 ± 0.04 M⊙, M2 = 1.45 ± 0.03 M⊙, R1 = 1.69 ± 0.03 R⊙, R2 = 1.43 ± 0.03 R⊙, L1 = 8.21 ± 0.90 L⊙ and L2 = 3.64 ± 0.60 L⊙. The distance to TX Her was calculated as 155 ± 10 pc, taking into account interstellar extinction. The position of the components of TX Her in the HR diagram are also discussed. The components are young stars with an age of ～500 Myr.  相似文献   

11.
The abundance of HDO above the clouds in the dayside atmosphere of Venus was measured by ground-based 2.3 μm spectroscopy over 4 days. This is the first HDO observation above the clouds in this wavelength region corresponding to a new height region. The latitudinal distributions found show no clearly defined structure. The disk-averaged mixing ratio is 0.22 ± 0.03 ppm for a representative height region of 62–67 km. This is consistent with measurements found in previous studies. Based on previous H2O measurements, the HDO/H2O ratio is found to be 140 ± 20 times larger than the telluric ratio. This lies between the ratios of 120 ± 40 and 240 ± 25, respectively, reported for the 30–40 km region by ground-based nightside spectroscopy and for the 80–100 km region by solar occultation measurement on board the Venus Express.  相似文献   

12.
《New Astronomy》2007,12(6):461-470
We present results of a study that combines UBVI photometry, MK spectral classification and proper motions in the area of the, up to now unknown, open cluster Ruprecht 58 at the Puppis region. Star counts from the 2MASS data catalog together with the analysis of CCD UBVI photometry demonstrate that it is a real open cluster with 9′ size approximately. The cluster is placed at a distance of 3.9 kpc and is about 250 Myr old with mean reddening E(B−V) = 0.33 mag. Proper motions confirm Ruprecht 58 is a real cluster with mean absolute proper motions μαcosδ = −2.77 ± 0.45 mas/yr and μδ = 4.54 ± 0.45 mas/yr in the magnitude range 13.5 < V < 14.5 and μαcosδ = −2.70 ± 0.32 mas/yr and μδ = 3.19 ± 0.32 mas/yr in the range 14.5 < V < 16.0. The computation of the cluster mass spectrum slope yielded x = 1.8 in the mass range from ≈1.4 to ≈4m⊙.  相似文献   

13.
Here we report the serendipitous identification of a bright optical transient in the vicinity of the dwarf elliptical galaxy M 32 (NGC 221). This transient (MONS OT J004240.69+405142.0) was detected using filtered CCD imaging, about 20 arcsec southwest from the core of M 32, at equatorial coordinates α = 00:42:40.69 ± 0.05, δ = +40:51:42.0 ± 0.5, between 04:20:16 and 04:21:46 UT on June 22, 2007. A detailed analysis of the intensity profile of the feature suggests that it is of stellar nature with apparent visual magnitude 9.69 ± 0.15 which gives an absolute magnitude of ?14.7 ± 0.3 if the feature is located in M 31/M 32. Under the assumption of the event reported here being of cosmic origin and although no correlation with GRBs in time or space has been found, the behaviour of the optical transient appears to resemble that of the recently observed GRB 080319B: very fast ascent and decay of several magnitudes within a few minutes. If this interpretation is correct, the afterglow decay was extremely rapid, decreasing by more than 5 mag. in about 2 min, α = 2.4. Given its properties, the event is a possible orphan GRB optical afterglow candidate originated beyond the Local Group. Alternative explanations are also discussed.  相似文献   

14.
This study presents the absolute parameters of the contact binary system V376 And. CCD photometric observations were made at the Çanakkale Onsekiz Mart University Observatory in 2004. The instrumental magnitudes of all observed stars were converted into standard magnitudes. New BV light curves of the system were analysed using the Wilson–Devinney method supplemented with a Monte Carlo type algorithm. Since there are large asymmetries between maxima (i.e., O’Connell effect) in these light curves, two different models (one with a cool spot and one with a hot spot) were applied to the photometric data. The best fit, which was obtained with a large hot spot on the secondary component, gives V376 And as an A sub-type contact binary in poor thermal contact and a small value of the filling factor (f ≈ 0.07). Combining the solutions of our light curves and Rucinski et al. (2001)’s radial velocity curves, the following absolute parameters of the components were determined: M1 = 2.44 ± 0.04 M⊙, M2 = 0.74 ± 0.03 M⊙, R1 = 2.60 ± 0.03 R⊙, R2 = 1.51 ± 0.02 R⊙, L1 = 40 ± 4 L⊙ and L2 = 5 ± 1 L⊙. We also discuss the evolution of the system, which appears to have an age of 1.6 Gyr. The distance to V376 And was calculated as 230 ± 20 pc from this analysis, taking into account interstellar extinction.  相似文献   

15.
Using the Hilbert–Huang Transform (HHT) method, we investigate the periodicity in the monthly mean flare indices from 1966 to 2007 (corresponding to almost four complete solar cycles), calculated by T. Atac and A. Ozguc. The results show as following. (1) The periods of 9.37 ± 2.53, 11.8 ± 0.172 and 23.6 ± 0.316 years are found to be statistically significant in the flare index. The most eminent period is 9.37 ± 2.53 years. (2) Other periods of 0.237 ± 0.196 years (86.6 ± 71.6 days), 0.525 ± 0.0508 years (191 ± 18.5 days), 1.05 ± 0.478 years (383 ± 174 days) and 2.37 ± 0.395 years are below the 99% confidence level line, suggesting they are due to stochastic random noise.  相似文献   

16.
We obtained multi-colour light curves of the overcontact binary system HH Boo and analysed the orbital period variation of the system. Our analysis tentatively indicates either mass transfer from the secondary to the primary or mass loss from the system at a rate of -5.04 × 10−7 M⊙ per year. Through a combined analysis of the published radial velocity curve and light curves, we determined an inclination (i) of 69°.71 ± 0°.16 and a semi-major axis (a) of 2.246 ± 0.064 R⊙ for HH Boo. The masses of the primary and secondary components were found to be 0.92 ± 0.08 M⊙ and 0.58 ± 0.06 M⊙, respectively. The radius determined for the primary was 0.98 ± 0.03 R⊙, while that determined for the secondary was 0.80 ± 0.02 R⊙. We demonstrated that HH Boo is most likely a member of the A-type subclass of W UMa binaries.  相似文献   

17.
The results obtained from unfiltered photometric CCD observations of AY Psc made during 17, 20 and 12 nights, respectively, in 2003, 2004 and 2005 are presented. A period of 0.21732 ± 0.00001 d was detected in the data. This period is consistent with the previously proposed orbital period of Porb = 0.2173209 d ((Diaz and Steiner, 1990)). Since this period was present in the light curves taken in all three years, with no apparent change in its value or amplitude, it is interpreted as the orbital period of this binary system. In addition, quasi-periodicities of 0.2057 ± 0.0001 d, 0.2063 ± 0.0001 d, 0.2072 ± 0.0001 d for the years 2003, 2004 and 2005, respectively, were also discovered. These periods were interpreted as negative superhump periods and it was seen that they changes from year to year. Therefore AY Psc is then classified as a negative superhump system.  相似文献   

18.
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19.
The linear nonadiabatic oscillations for evolutionary models of 0.6- 3M8 stars are calculated by using a nonlocal and time-dependent convection theory. The results show that in the HR diagram the pulsation-unstable low- temperature stars on the right side of instability strip can be divided into two groups. One group indicates the Sun-like oscillation stars composed of the main- sequence dwarfs, sub-giants and red giants (RGs) of low and intermediate lu- minosities, which are unstable in the intermediate- and high-order (n ≥ 12) p- modes, and stable in the low-order (n ≤ 5) p-modes. Another group indicates the Mira-like stars composed of the bright RGs and asymptotic giant branch (AGB) stars, which are just contrary to Sun-like stars, unstable in low-order (n ≤ 5) p-modes and stable in the intermediate- and high-order (n ≥ 12) p-modes. The oscillations for the red edge of Cepheid (δ Scuti) instability strip, Sun-like and Mira-like stars can be explained uniformly by the coupling between convection and oscillation (CCO). For the low-temperature stars on the right side of in- stability strip, CCO is the dominant excitation and damping mechanism of the oscillations of low- and intermediate-order p-modes, and the turbulent stochas- tic excitation becomes important only for the high-order p-modes of Sun-like oscillations.  相似文献   

20.
We have examined thermal emission from 240 active or recently-active volcanic features on Io and quantified the magnitude and distribution of their volcanic heat flow during the Galileo epoch. We use spacecraft data and a geological map of Io to derive an estimate of the maximum possible contribution from small dark areas not detected as thermally active but which nevertheless appear to be sites of recent volcanic activity. We utilize a trend analysis to extrapolate from the smallest detectable volcanic heat sources to these smallest mapped dark areas. Including the additional heat from estimates for “outburst” eruptions and for a multitude of very small (“myriad”) hot spots, we account for ～62 × 1012 W (～59 ± 7% of Io’s total thermal emission). Loki Patera contributes, on average, 9.6 × 1012 W (～9.1 ± 1%). All dark paterae contribute 45.3 × 1012 W (～43 ± 5%). Although dark flow fields cover a much larger area than dark paterae, they contribute only 5.6 × 1012 W (～5.3 ± 0.6%). Bright paterae contribute ～2.6 × 1012 W (～2.5 ± 0.3%). Outburst eruption phases and very small hot spots contribute no more than ～4% of Io’s total thermal emission: this is probably a maximum value. About 50% of Io’s volcanic heat flow emanates from only 1.2% of Io’s surface. Of Io’s heat flow, 41 ± 7.0% remains unaccounted for in terms of identified sources. Globally, volcanic heat flow is not uniformly distributed. Power output per unit surface area is slightly biased towards mid-latitudes, although there is a stronger bias toward the northern hemisphere when Loki Patera is included. There is a slight favoring of the northern hemisphere for outbursts where locations were well constrained. Globally, we find peaks in thermal emission at ～315°W and ～105°W (using 30° bins). There is a minimum in thermal emission at around 200°W (almost at the anti-jovian longitude) which is a significant regional difference. These peaks and troughs suggest a shift to the east from predicted global heat flow patterns resulting from tidal heating in an asthenosphere. Global volcanic heat flow is dominated by thermal emission from paterae, especially from Loki Patera (312°W, 12°N). Thermal emission from dark flows maximises between 165°W and 225°W. Finally, it is possible that a multitude of very small hot spots, smaller than the present angular resolution detection limits, and/or cooler, secondary volcanic processes involving sulphurous compounds, may be responsible for at least part of the heat flow that is not associated with known sources. Such activity should be sought out during the next mission to Io.  相似文献   

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