Anisotropic angular broadening in the solar wind     

A. K. R. Anantharamaiah  B. Pradeep Gothoskar  C. T. J. Cornwell 《Astrophysics and Space Science》1996,243(1):77-81

We present Very Large Array observations at wavelengths of 2, 3.5, 6, and 20 cm, of angular broadening of radio sources due to the solar wind in the region 2–16 solar radii. Angular broadening is anisotropic with axial ratios in the range 2–16. Larger axial ratios are observed preferentially at smaller solar distances. Assuming that anisotropy is due to scattering blobs elongated along magnetic field lines, the distribution of position angles of the elliptically broadened images indicates that the field lines are non-radial even at the largest heliocentric distances observed here. At 5R , the major axis scattering angle is 0.7 at =6 cm and it varies with heliocentric distance asR ^–1.6. The level of turbulence, characterized by the wave structure function at a scale of 10 km along the major axis, normalized to =20 cm, has a value 20±7 at 5R and varies with heliocentric distance asR ^–3. Comprison with earlier results suggest that the level of turbulence is higher during solar maximum. Assuming a power-law spectrum of electron density fluctuations, the fitted spectral exponents have values in the range 2.8–3.4 for scales sizes between 2–35 km. The data suggests temporal fluctuations (of up to 10%) in the spectral exponent on a time scale of a few tens of minutes. The observed structure functions at different solar distances do not show any evidence for an inner scale; the upper limits are 1 km at 2R and 4 km at 13R . These upper limits are in conflict with earlier determinations and may suggest a reduced inner scale during solar maximum.  相似文献   

Galactic kinematics from OB3 stars with distances determined from interstellar Ca II lines     

V. V. Bobylev  A. T. Bajkova 《Astronomy Letters》2011,37(8):526-535

Based on data for 102 OB3 stars with known proper motions and radial velocities, we have tested the distances derived by Megier et al. from interstellar Ca II spectral lines. The internal reconciliation of the distance scales using the first derivative of the angular velocity of Galactic rotation Ω′₀ and the external reconciliation with Humphreys’s distance scale for OB associations refined by Mel’nik and Dambis show that the initial distances should be reduced by ≈20%. Given this correction, the heliocentric distances of these stars lie within the range 0.6–2.6 kpc. A kinematic analysis of these stars at a fixed Galactocentric distance of the Sun, R ₀ = 8 kpc, has allowed the following parameters to be determined: (1) the solar peculiar velocity components (u _⊙, v _⊙, ω _⊙) = (8.9, 10.3, 6.8) ± (0.6, 1.0, 0.4) km s⁻¹; (2) the Galactic rotation parameters Ω₀ = −31.5 ± 0.9 km s⁻¹ kpc⁻¹, Ω′₀ = +4.49 ± 0.12 km s⁻¹ kpc⁻², Ω″₀ = −1.05 ± 0.38 km s⁻¹ kpc⁻³ (the corresponding Oort constants are A = 17.9 ± 0.5 km s⁻¹ kpc⁻¹, B = −13.6 ± 1.0 km s⁻¹ kpc⁻¹ and the circular rotation velocity of the solar neighborhood is |V ₀| = 252 ± 14 km s⁻¹); (3) the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f _R = −12.5±1.1 km s⁻¹ and f _ϑ = 2.0 ± 1.6 km s⁻¹; the pitch angle for the two-armed spiral pattern i = −5.3° ± 0.3°, with the wavelength of the spiral density wave at the solar distance being λ = 2.3 ± 0.2 kpc; the Sun’s phase in the spiral wave x _⊙ = −91° ± 4°.  相似文献   

Evolution of Coronal Mass Ejections in the Inner Heliosphere: A Study Using White-Light and Scintillation Images     

P. K. Manoharan 《Solar physics》2006,235(1-2):345-368

Knowledge of the radial evolution of the coronal mass ejection (CME) is important for the understanding of its arrival at the near-Earth space and of its interaction with the disturbed/ambient solar wind in the course of its travel to 1 AU and further. In this paper, the radial evolution of 30 large CMEs (angular width > 150^∘, i.e., halo and partial halo CMEs) has been investigated between the Sun and the Earth using (i) the white-light images of the near-Sun region from the Large Angle Spectroscopic Coronagraph (LASCO) onboard SOHO mission and (ii) the interplanetary scintillation (IPS) images of the inner heliosphere obtained from the Ooty Radio Telescope (ORT). In the LASCO field of view at heliocentric distances R≤30 solar radii (R_⊙), these CMEs cover an order of magnitude range of initial speeds, V_CME≈260–2600 km s⁻¹. Following results have been obtained from the speed evolution of these CMEs in the Sun–Earth distance range: (1) the speed profile of the CME shows dependence on its initial speed; (2) the propagation of the CME goes through continuous changes, which depend on the interaction of the CME with the surrounding solar wind encountered on the way; (3) the radial-speed profiles obtained by combining the LASCO and IPS images yield the factual view of the propagation of CMEs in the inner heliosphere and transit times and speeds at 1 AU computed from these profiles are in good agreement with the actual measurements; (4) the mean travel time curve for different initial speeds and the shape of the radial-speed profiles suggest that up to a distance of ∼80 R_⊙, the internal energy of the CME (or the expansion of the CME) dominates and however, at larger distances, the CME's interaction with the solar wind controls the propagation; (5) most of the CMEs tend to attain the speed of the ambient flow at 1 AU or further out of the Earth's orbit. The results of this study are useful to quantify the drag force imposed on a CME by the interaction with the ambient solar wind and it is essential in modeling the CME propagation. This study also has a great importance in understanding the prediction of CME-associated space weather at the near-Earth environment.  相似文献   

Polar Plume Anatomy: Results of a Coordinated Observation     

C. E. DeForest  J. T. Hoeksema  J. B. Gurman  B. J. Thompson  S. P. Plunkett  R. Howard  R. C. Harrison  D. M. Hasslerz 《Solar physics》1997,175(2):393-410

On 7 and 8 March 1996, the SOHO spacecraft and several other space- and ground-based observatories cooperated in the most comprehensive observation to date of solar polar plumes. Based on simultaneous data from five instruments, we describe the morphology of the plumes observed over the south pole of the Sun during the SOHO observing campaign. Individual plumes have been characterized from the photosphere to approximately 15 R⊙ yielding a coherent portrait of the features for more quantitative future studies. The observed plumes arise from small (∼ 2-5 arc sec diameter) quiescent, unipolar magnetic flux concentrations, on chromospheric network cell boundaries. They are denser and cooler than the surrounding coronal hole through which they extend, and are seen clearly in both Feix and Fexii emission lines, indicating an ionization temperature between 1.0–1.5 x 10⁶ K. The plumes initially expand rapidly with altitude, to a diameter of 20–30 Mm about 30 Mm off the surface. Above 1.2 R⊙ plumes are observed in white light (as ‘coronal rays’) and extend to above 12 R⊙. They grow superradially throughout their observed height, increasing their subtended solid angle (relative to disk center) by a factor of ∼10 between 1.05 R⊙ and 4–5 R⊙ and by a total factor of 20–40 between 1.05 R⊙ and 12 R⊙. On spatial scales larger than 10 arc sec, plume structure in the lower corona (R < 1.3 R⊙) is observed to be steady-state for periods of at least 24 hours; however, on spatial scales smaller than 10 arc sec, plume XUV intensities vary by 10–20% (after background subtraction) on a time scale of a few minutes. (Dr. Hassler is now employed by Southwest Research Institute, Boulder, CO)  相似文献   

Molecular Clouds Toward a New OB Association in Pup-CMa     

J. May  A. L. Gyulbudaghian  H. Alvarez 《Astrophysics》2005,48(4):411-421

We have mapped 16 molecular clouds toward a new OB association in the Pup-CMa region to derive their physical properties. The observations were carried out in the ¹²CO (J = 1 – 0) line with the Southern millimetre-wave Telescope at Cerro Tololo, Chile. Distances have been determined kinematically using the rotation curve of Brand with R_⊙ = 8.5 kpc and V_⊙ = 220 km/s. Masses have been derived adopting a CO luminosity to H₂ conversion factor X = 3.8 . 10²⁰ molecules cm^-2 (K km/s)^-1. The observed mean radial velocity of the clouds is comparable with the mean radial velocity of stars composing an OB association in Pup-CMa; it is in favor of the close connection of clouds with these stars. __________ Published in Astrofizika, Vol. 48, No. 4, pp. 491–501 (October–December, 2005).  相似文献   

Evidence for a coronal magnetic bottle at 10 solar radii     

Kenneth H. Schatten 《Solar physics》1970,12(3):484-491

The Faraday rotation of a radio source (Pioneer 6) occulted by the solar corona has been measured by Levy et al. (1969). During the course of these measurements, three large-scale transient phenomena were observed. These events were preceded by subflares and class 1 flares. These transient events are interpreted as evidence for a coronal magnetic bottle at 10 R _⊙. The velocity of propagation for the disturbance is set at 200 km/sec; the dimension of the region, 10 R _⊙; field strength at 10 R _⊙, 0.02 G; particle density, 2.0 × 10⁴/cm³; Alfvén speed, 320 km/sec. From the nature of the observations and the lack of related effects from similar flares on the interplanetary sector pattern observed at 1 AU, it is suggested that such coronal magnetic bottles expand to perhaps 10–30 R _⊙ and then contract to a few solar radii. Such a phenomena is evidence for an expansion of the corona with a sub-Alfvénic velocity. It is further suggested that such magnetic bottles may be important in the storage and diffusion of solar generated cosmic ray particles. NAS-NRC Postdoctoral Resident Research Associate.  相似文献   

Changes in the Sun’s mass and gravitational constant estimated using modern observations of planets and spacecraft     

E. V. Pitjeva  N. P. Pitjev 《Solar System Research》2012,46(1):78-87

More than 635 thousand positional observations of planets and spacecraft of various types (mostly radiotechnical ones, 1961–2010) were used to estimate possible changes in the gravitational constant, Sun’s mass, and semi-major axes of planetary orbits, as well as the associated value of the astronomical unit. The observations were analyzed based on the EPM2010 ephemerides constructed at the Institute of Applied Astronomy (Russian Academy of Sciences) in a post-Newtonian approximation as a result of simultanious numerical integration of the equations of motion of nine major planets, the Sun, the Moon, asteroids, and trans-Neptunian objects. The heliocentric gravitational constant GM _⊙ was found to vary with a rate of (GṀ _⊙/GM _⊙ = (−5.0 ± 4.1)) × 10⁻¹⁴ per year (at the 3σ level). The positive secular changes in the semimajor axes ȧ _i /a _i were found for Mercury, Venus, Mars, Jupiter, and Saturn provided by high-precision observations. These changes also correspond to the decrease in the heliocentric gravitational constant. The changing of GM _⊙, itself is probably caused by the loss of the mass M _⊙ of the Sun due to its radiation and solar wind; these effects are partly compensated by the material falling onto the Sun. Allowing for the maximum bounds on the possible change in the Sun’s mass M _⊙, it has been found from the change obtained in GM _⊙ that the annual change Ġ/G of the gravitational constant G falls within the interval −4.2 × 10⁻¹⁴ < ȧ/G < +7.5 × 10⁻¹⁴ with a 95% probability. The astronomical unit (AU) is connected by its definition only with the heliocentric gravitational constant. The decrease of GM _⊙ obtained in this paper should correspond to a secular decrease in the AU. It is shown, however, that the modern level of accuracy does not allow us to determine a change in the AU. The attained posibility of determining changes in GM _⊙ using high-accuracy observations encourages us to have a relation between GM _⊙ and the AU fixed for a certain moment in time, since it is inconvenient to have a time-dependent length for the AU.  相似文献   

Video Observations Of Leonids 1999     

Molau  Sirko  Rendtel  Jürgen  Bellot-Rubio  Luis Ramon 《Earth, Moon, and Planets》1999,87(1):1-10

We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main peak occured at 02:03 UT (λ_⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53 UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors with a turning point close to +3^m, which corresponds to meteoroids of approximately 10^-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ_⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Hβ luminosity of extragalactic objects and evolution of galaxies     

R. K. Thakur  R. K. Sood 《Astrophysics and Space Science》1982,88(1):99-114

Hourly interplanetary proton plasma data, measured by Helios-1 and Helios-2 heliocentric satellites over the period extending between the sunspot minimum and maximum of the 21rst solar cycle are analysed. This analysis gives an emphasis in the presence of a third type solar wind (intermediate) at 450 km s^–1, appearing at solar minimum, during which large coronal holes are dominating in the Sun. This type of solar wind is hardly to be observed during the solar maximum period.Both Helios-1 and Helios-2 data give an average speed of the slow solar wind of 350 km s^–1 for the period between these two extremes of solar activities.After correlation of the plasma temperature with its speed in different heliocentric distances, it comes out the stronger heating which takes place in distances shorter than 0.6 AU than in distances between 0.6 and 1.0 AU.A different behaviour of the radial proton temperature gradient in different solar activities appears after the calculation of the gradients as a function of solar wind speed and radial distance.  相似文献   

Lasco Observations of Disconnected Magnetic Structures Out to Beyond 28 Solar Radii During Coronal Mass Ejections     

G. M. Simnett  S. J. Tappin  S. P. Plunkett  D. K. Bedford  C. J. Eyles  O. C. St. Cyr  R. A. Howard  G. E. Brueckner  D. J. Michels  J. D. Moses  D. Socker  K. P. Dere  C. M. Korendyke  S. E. Paswaters  D. Wang  R. Schwenn  P. Lamy  A. Llebaria  M. V. Bout 《Solar physics》1997,175(2):685-698

Two coronal mass ejections have been well observed by the LASCO coronagraphs to move out into the interplanetary medium as disconnected plasmoids. The first, on July 28, 1996, left the Sun above the west limb around 18:00 UT. As it moved out, a bright V-shaped structure was visible in the C2 coronagraph which moved into the field-of-view of C3 and could be observed out to beyond 28 solar radii. The derived average velocity in the plane of the sky was 110 ± 5 km s^-1 out to 5 solar radii, and above 15 solar radii the velocity was 269 ± 10 km s^-1. Thus there is evidence of some acceleration around 6 solar radii. The second event occurred on November 5, 1996 and left the west limb around 04:00 UT. The event had an average velocity in the plane of the sky of ∼54 km s^-1 below 4 R⊙, and it accelerated rapidly around 5 R⊙ up to 310 ± 10 km s^-1. In both events the rising plasmoid is connected back to the Sun by a straight, bright ray, which is probably a signature of a neutral sheet. In the November event there is evidence for multiple plasmoid ejections. The acceleration of the plasmoids around a projected altitude of 5 solar radii is probably a manifestation of the source surface of the solar wind. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004994214697  相似文献   

The morphological and spectral investigation of the galaxies Kaz 5, Kaz 92, and Kaz 390     

V. Zh. Adibekyan  M. A. Kazarian  E. L. Karapetian 《Astrophysics》2009,52(1):54-65

The results of morphological and spectral study of the galaxies Kaz 5, Kaz 92, and Kaz 390 are presented. The observations were made on the 2.6-m telescope at the Byurakan Observatory with the VAGR microlenses spectrograph. Isophotes of the images of the galaxies are constructed in the Hα, [NII] λλ6584 , 6548, and [SII] λλ6731, 6717 emission lines and in the continuum. The masses of Kaz 5 and Kaz 92 are determined to be 8.6 × 10⁸ M_⊙ and 6.1 × 10⁹ M_⊙ , respectively. The mass of the gaseous component in the centers of regions I and IV of Kaz 390, which encompass a 1 pixel area, are also determined. The morphological structure of the central region of Kaz 5 in the observed spectral range, λλ6400–6800?, differs completely from the structure of the same part of the galaxy observed with the 6-m and 2.5-m telescopes. It is shown that these differences in the structure in images of Kaz 5 are mostly explained by the comparatively low resolution of the telescope in combination with the VAGR spectrograph. Absorbing matter also contributes to this effect. It is also shown that a “deficit” of nitrogen has been observed in the region of Kaz 390 studied here (a circle of diameter 40″). Translated from Astrofizika, Vol. 52, No. 1, pp. 63–74 (February 2009).  相似文献   

Observations of hydrogen deficient binary Upsilon sagittarii     

N. Kameswara Rao  V. R. Venugopal 《Journal of Astrophysics and Astronomy》1985,6(2):101-112

The absolute magnitudeM _v of the hydrogen deficient binary υ Sgr has been estimated as -4.8 ± 1.0 from the distribution of the interstellar reddening, polarization and interstellar lines of the surrounding stars. From the ANS observations obtained at the time of the secondary eclipse, it appears that the hotter secondary is surrounded by a disc with colours of a B8-B9 star. The λ 1550 CIv absorption line arising in the stellar wind does not show any change in strength during the secondary minimum. The upper limit to the mass-loss rate from the high temperature wind is estimated as ≤ 5 × 10^-7 M⊙ yr^-1 from the 2 cm and 6 cm radio observations. Based on observations obtained with the Astronomical Netherlands Satellite and VLA. The National Radio Astronomy Observatory’s Very Large Array at Socorro, New Mexico is operated by Associated Universities Inc. under contract with the National Science Foundation.  相似文献   

The Variation of Solar Wind Correlation Lengths Over Three Solar Cycles     

R. T. Wicks  M. J. Owens  T. S. Horbury 《Solar physics》2010,262(1):191-198

We present the results of a study of solar wind velocity and magnetic field correlation lengths over the last 35 years. The correlation length of the magnetic field magnitude λ _|B| increases on average by a factor of two at solar maxima compared to solar minima. The correlation lengths of the components of the magnetic field l_BXYZ\lambda_{B_{XYZ}} and of the velocity l_VYZ\lambda_{V_{YZ}} do not show this change and have similar values, indicating a continual turbulent correlation length of around 1.4×10⁶ km. We conclude that a linear relation between λ _|B|, VB ², and Kp suggests that the former is related to the total magnetic energy in the solar wind and an estimate of the average size of geoeffective structures, which is, in turn, proportional to VB ². By looking at the distribution of daily correlation lengths we show that the solar minimum values of λ _|B| correspond to the turbulent outer scale. A tail of larger λ _|B| values is present at solar maximum causing the increase in mean value.  相似文献   

Photometric study of the W UMa eclipsing binaries VW LMi and BX Dra     

F. Sánchez-Bajo  E. García-Melendo  J. M. Gómez-Forrellad 《Astrophysics and Space Science》2007,312(3-4):151-159

New ephemeris and the absolute parameters—masses, radii and luminosities—of the contact systems VW LMi and BX Dra have been obtained, by means of the analysis of the minima data available in the literature (for the determination of the ephemeris) and combining the previously published spectroscopic information and the results of the Wilson-Devinney method using photometric data (for the determination of the absolute parameters). The VW LMi O−C analysis confirms the multiplicity of the system detected previously from the spectroscopic data. Masses of the VW LMi contact system primary and secondary components are 1.67 ± 0.02M _⊙ and 0.70 ± 0.02M _⊙, respectively. The corresponding radii are 1.709 ± 0.007R _⊙ and 1.208 ± 0.006R _⊙, respectively. For the BX Dra contact system the masses are 2.19 ± 0.13M _⊙ and 0.63 ± 0.06M _⊙, and the radii, 2.13 ± 0.04R _⊙ and 1.26 ± 0.03R _⊙, for the primary and secondary, respectively. In both cases, the estimated luminosities seem to be slightly greater that the values derived from the Hipparcos distances.  相似文献   

Dust Activity in Comet 67P/Churyumov–Gerasimenko from February 20 to April 20, 2003     

L. M. Lara  J. de León  J. Licandro  P. J. Gutiérrez 《Earth, Moon, and Planets》2005,97(1-2):165-175

Broadband imaging of Comet 67P/Churyumov–Gerasimenko has provided more data on the characterisation of the target of the ESA Rosetta Mission. The comet monitoring between r _h=2.37 and r _h=2.78 AU postperihelion shows a prominent dust coma which extends up to ≈ 25,000 km from the nucleus, and a long dust structure in approximately anti-tail direction, reaching at least 230,000 km, identified as a neck-line structure. The non-isotropic dust emission is detected from the structures in the inner coma, and it is reflected on the slope of linear fits of surface brightness profiles vs. cometocentric projected distance in log–log representation as m ≈ 0.83−0.941. Besides the long dust spike at position angle of 295°, the morphological study of the dust coma confirms the presence of two structures at position angles of 95 and 195° where the overabundance of dust can be as high as 50% at ρ ≤ 30,000 km. The A f ρ parameter derived from our R broadband data is 26.0 and 29.8 cm at r _h=2.37 and 2.48 AU postperihelion. The dust reflectivity S′(λ), a measurement of the dust colour, is 0.061±0.019, a rather neutral colour.  相似文献   

WR 140 (=V1687 Cyg): Infrared photometry, 2001–2010     

O. G. Taranova  V. I. Shenavrin 《Astronomy Letters》2011,37(1):30-39

We present the results of our infrared observations of WR 140 (=V1687 Cyg) in 2001–2010. Analysis of the observations has shown that the J brightness at maximum increased near the periastron by about 0 ^m .3; the M brightness increased by ∼2 ^m in less than 50 days. The minimum J brightness and the minimum L and M brightnesses were observed 550–600 and 1300–1400 days after the maximum, respectively. The JHKLM brightness minimum was observed in the range of orbital phases 0.7–0.9. The parameters of the primary O5 component of the binary have been estimated to be the following: R(O5) ≈ 24.7R _⊙, L(O5) ≈ 8 × 10⁵ L _⊙, and M _bol(O5) ≈ −10 ^m . At the infrared brightness minimum, T _g ∼ 820–880 K, R _g ≈ 2.6 × 10⁵ R _⊙, the optical depth of the shell at 3.5 μm is ∼5.3 × 10⁻⁶, and its mass is ≈1.4 × 10⁻⁸ M _⊙. At the maximum, the corresponding parameters are ∼1300 K, 8.6 × 10⁴ R _⊙, ∼2 × 10⁻⁴, and ∼6 × 10⁻⁸ M _⊙; the mean rate of dust inflow (condensation) into the dust structure is ∼3.3 × 10⁻⁸ M _⊙ yr⁻¹. The mean escape velocity of the shell from the heating source is ∼10³ km s⁻¹ and the mean dispersal rate of the shell is ∼1.1 × 10⁻⁸ M _⊙ yr⁻¹.  相似文献   

Scaling Properties of X-ray Clusters: The Chandra View     

Paolo Tozzi 《Astrophysics and Space Science》2004,294(1-2):45-50

The study of X-ray clusters of galaxies, started 30 years ago, has revealed an increasing complexity in the thermodynamics of the X-ray emitting intracluster medium (ICM) as long as the sensitivity and the resolution of the X-ray satellites increased. At the same time, deep surveysdetected several, unexpected, high-z clusters. Here we focus on the Chandra observations of the most distant X-ray selected clusters (0.3 < z < 1.3), in order to constrain their thermodynamic evolution. The X-ray scaling properties show hints of negative evolution in the luminosity–temperature and M _gas–temperature relations, and a positive evolution in the entropy–temperature relation. We find that the mean iron abundance at 〈z〉 = 0.8 is Z _Fe = 0.25^+0.04 _−0.06 Z _⊙, and at 〈z〉 ∼ 1.2 is Z _Fe = 0.35^+0.06 _−0.05 Z _⊙, both measures consistent with no evolution with respect to the local value Z _Fe≃ 0.3 Z _⊙. These results can provide interesting constraints on the thermodynamics of the ICM at large look back times, pointing towards a redshift z ≳ 2 for the onset of non-gravitational processes.  相似文献   

CCD photometry inVRI bands of the galactic cluster NGC 2818     

R. Surendiranath  N. Kameswara Rao  Ram Sagar  J. S. Nathan  K. K. Ghosh 《Journal of Astrophysics and Astronomy》1990,11(2):151-166

bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M) ₀ = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1) × 10₈ years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor mass of the planetary nebula on the main sequence is ≥2.5M_⊙ Based on observations obtained with the Vainu Bappu Telescope.  相似文献   

XMM-Newton observations of the isolated neutron star 1RXS J214303.7+065419/RBS1774     

Mark Cropper  Silvia Zane  Roberto Turolla  Luca Zampieri  Matteo Chieregato  Jeremy Drake  Aldo Treves 《Astrophysics and Space Science》2007,308(1-4):161-166

We report XMM-Newton observations of the isolated neutron star RBS1774 and confirm its membership as an XDINS. The X-ray spectrum is best fit with an absorbed blackbody with temperature kT=101 eV and absorption edge at 0.7 keV. No power law component is required. An absorption feature in the RGS data at 0.4 keV is not evident in the EPIC data, but it is not possible to resolve this inconsistency. The star is not seen in the UV OM data to m _AB ∼21. There is a sinusoidal variation in the X-ray flux at a period of 9.437 s with an amplitude of 4%. The age as determined from cooling and magnetic field decay arguments is 10⁵–10⁶ yr for a neutron star mass of 1.35–1.5 M_⊙.   相似文献   

Two new LBV candidates in the M 33 galaxy     

A. F. Valeev  O. N. Sholukhova  S. N. Fabrika 《Astrophysical Bulletin》2010,65(4):381-389

We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates were selected from the Massey et al. catalog based on the following criteria: emission in H _α , V<18^./m 5 and 0_.^m 35 < (B - V) < 1_.^m 2. The spectra of both stars reveal a broad and strong H _α emission with extended wings (770 and 1000 kms⁻¹). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L_⊙) = 6.0–6.2 with the value of interstellar extinction A _V = 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero Age Main Sequence is M∼ 60–80 M_⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L_⊙) = 6.3 − 6.6, the value of interstellar extinction is A _V = 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M_⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two thermal components with the temperatures T_warm ∼ 1000K and T_cold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and broad H α emissions allow classifying the studied objects as LBV candidates.  相似文献