A kinematic study of the Galaxy

Using the proper motion and parallax data for 1011 O-B stars in the Hipparcos Catalogue we have derived the Oort constants, A = 17.60 ± 0.21 (km/s)/kpc, B = −14.62 ± 0.20 (km/s)/kpc, and a solar velocity V = 16.7 ± 0.10 km/s in the direction l = 45.3° ± 2.8°, b = 21.0° ± 2.3°. For a galactocentric distance of the sun of R₀ = 8.5 kpc, we then get a galactic rotational velocity of the solar neighbourhood of V_lsr = 273.9 km/s, obviously much higher than the IAU published value of 220 km/s. We have investigated the cause for this difference.     

Galactic kinematics derived from classical cepheids

On the basis of radial velocity and Hipparcos proper motion data, we have analyzed the galactic kinematics of classical Cepheids. Using the 3-D Ogorodnikov-Milne model we have determined the rotational velocity of the Galaxy to be V₀ = 240.5 ± 10.2 km/s, on assuming a glactocentric distance of the Sun of R₀ = 8.5 kpc. The results clearly indicate a contracting motion in the solar neighbourhood of (∂V_θ∂θ)/R = −2.60 ± 1.07 km s⁻¹ kpc⁻¹, along the direction of galactic rotation. Possible reason for this motion is discussed. The solar motion found here is S = 18.78 ± 0.86 km/s in the direction l = 54.4° ± 2.9° and b = +26.6° ± 2.6°.     

Observation and Study of the CO, CO, HCO and N2H Molecular Lines Towards IRAS 02232+6138

Using the 13.7 m millimeter-wave telescope at the Qinghai Station of Purple Mountain Observatory, we have made observations of ¹³CO, C¹⁸O, HCO⁺ and N₂H⁺ molecular lines towards IRAS 02232+6138. As the excitation density of the probe molecule increases from ¹³CO to HCO⁺, the size of the cloud core associated with IRAS 02232+6138 decreases from 2.40 pc to 0.54 pc, and the virial mass of the cloud core decreases from 2.2 × 10³M to 5.1 × 10²M. A bipolar molecular outflow is found towards IRAS 02232+6138. Using the power function n(r) ∝ r⁻ to fit the spatial density structure of the cloud core, we obtain the power-law index  = 2.3 − 1.2; and we find that, as the probed density increases, the power function becomes more flat. The abundance ratio of ¹³CO to C¹⁸O is 12.4 ± 6.9, comparable with the values 11.8 ± 5.9 for dark clouds and the values 9.0–15.6 for massive cores. The abundance of N₂H⁺ molecules is 3.5 ± 2.5 × 10⁻¹⁰, consistent with the value 1.0 − 5.0 × 10⁻¹⁰ for dark cloud cores and the value 1.2 − 12.8 × 10⁻¹⁰ for massive cores. The abundance of HCO⁺ molecules is 0.9 ± 0.5 × 10⁻⁹, close to the value 1.6 − 2.4 × 10⁻⁹ for massive cores. An increase of HCO⁺ abundance in the outflow region was not found. Combining with the IRAS data, the luminosity-mass ratio of the cloud core is obtained in the range 37–163(L/M). Based on the IRAS luminosity, it is estimated that a main-sequence O7.5 star is probably embedded in the IRAS 02232+6138 cloud core.     

Surface temperature of a rotating charged body

The surface temperature of a rotating, charged body is found separately under the Kerr-Newman metric and the vector graviton metric. Particular reference is made to pulsars. It is found that, 1) under the Kerr-Newman metric, the surface temperature rises from the poles to the equator, when the radius R of the body is greater than a certain critical value, r_n. When R= r_n, the surface temperature is uniform. When R < r_n, the above gradient is reversed. For pulsars, the equatorial temperature is some 3 × 10⁴ K higher than the polar temperature. 2) Under the Vector graviton field metric, a similar temperature differential exists, but it is much smaller in size.     

Adiabatic vibrational frequencies of local and nonlocal convection models of the sun

The eigen-vibrational frequencies of Xiong Da-run's nonlocal and local convection models of solar envelope are calculated and compared. The differences between the observational and theoretical vibrational frequencies are less than 1%. They can be divided into two isolated groups. For modes with l ≥ 60, all the differences between observed and theoretical eigen-vibrational frequencies are distributed in a narrow and inclined belt in the (Δv ≈ v)-diagram. This shows that the theoretical model of solar convective region can approximately reflect the intrinsic structure of the sun in the region of r = (0.70–0.95)R. The discrepancies between the theoretical and observational frequencies come from the outer layers. For modes with l < 60, the theoretical vibrational frequency is smaller than the observational one. This implies that the temperature of the upper part of the convectively unstable region is rather low. The frequency difference is more dispersed in the local convection model than in the nonlocal convection model. For the intermediate- and low-frequency ranges (v < 3000), the difference between the two models is small, while for the high-frequency range (v ≥ 3000) the frequency in the local model is higher than in the nonlocal model. This means that the temperature of the radiation region beneath the convective region is higher in the local convection model than in the nonlocal convection model. The nonlocal model is nearer to the observation than the local model.     

A combined photometric and spectroscopic solution for aa ursae majoris

From the photometric and spectroscopic data on AA UMa obtained by us in 1987 and 1986 and using the Wilson-Devinney program, we made a simultaneous solution. We found mass-ratio q = 1. 8157 ± 0.0099, M₁ = 0.85 M, M₂ = 1. 55 M , A = 3.39 R , R₁ = 1.50 R , and degree of over-contact f = 0.15 ± 0.01. Adding six minimum times obtained by us to the literature, a new epoch formula is derived: Min.I(J.D.Hel) = 2 446 885.1119+0.468 125 83 E.     

Spectroscopic orbits of eclipsing binaries: WX Cancri

We have determined for the first time a spectroscopic orbit for WX Cnc. The orbital elements are V₀ = +9.8 km/s, k₁ = 110.2 km/s, K₂ = 149.0 km/s, T_o = HJD 2446 480.0309. After combining with the published photometric results, we derive the the following absolute parameters: A = 6.32R, R₁ = 1.53R, R₂=1.18R, M₁ = 1.29 M, M₂ = 0.96M. The spectroscopic mass-ratio is q = 0.74.     

The H-alpha variations of Epsilon Aurigae from the second to the fourth contact

Epsilon Aurigae was observed in Mar., Aug., 1983 and Jan., Mar., 1984 with Reticon at coudé focus of the McDonald 2.7m and 2.1m telescopes. Fifty-six observations were taken over eight nights during 2nd to 4th contact.

The H shows noticeable variations in profile, radial velocity, and equivalent width of both absorption and emission components. A similar phenomenon was detected during the corresponding phase of the 1955 – 1957 eclipse.

A model is proposed, in which the primary is a FO supergiant surrounded by a thin ring (or disk) of radius R = 450R and rotating at velocity V_sini = 60 – 70 kms⁻¹. This is the major source of the H emission component. The secondary is a type B star surrounded by a very extended envelope (R = 1000 R) and its rotational speed is similar to that of the ring of the primary. The B star heats a portion of the envelope comparable in size with the primary with enough hydrogen atoms in the lowest excited states, which cause the absorption of the emission from the primary.     

Lithium depletion in the solar atmosphere

Using a complete non-local convection theory, we carried out the theoretical calculations of ⁷Li depletion of the solar convective envelope models with different convective parameters c₁ and c₂, and got a model of the solar convection zone consistent with the observed ⁷Li abundance and the depth of the solar convection zone determined by helioseismic techniques. The overshooting distance of effective non-local convective mixing of ⁷Li is very extensive, which is about 1.07H_P or 0.09R. However, the super-radiative temperature zone is much narrower, and it is only 0.20H_P or 0.016R.     

Rotational discontinuities in an anisotropic plasma

A general theory of rotational discontinuities is developed and the changes in the components of the plasma pressure, p_| and p, and in the magnetic induction, B, are found. For a given value of λ=(p_| − p) 4πμ/B² upstream only a limited range of downstream anisotropies are possible. If λ>0.6 upstream then isotropy is not possible downstream. Some special solutions are analysed and the identification of rotational discontinuities is the solar wind is discussed.     

The velocity field and X-ray spectrum of the flare of 1981 May 13

The H velocity field at 0516 UT during the eruption of the X1.5/3B flare in the active region E58 N11 (Boulder 3106) on 1981 May 13, obtained with the horizontal solar spectrograph of Yunnan Observatory is given in this paper. A comparative analysis of the velocity field with the magnetic field shows that the velocity field is related to the gradient and neutral line of the magnetic field and the brightness of the flare maximum changes in the velocity field of ±15 km/s occurs at the location of greatest magnetic field gradient.

The neutral line of the magnetic field (h = 0) basically matches the zero velocity line (v = 0) between the two bright ribbons. But they do not match between the two bright knots where the filament is twisted and ascends. The spectral lines show the sloping morphology, from which we deduced the dynamical parameters of the twist of the rising filament.     

Changes in thermospheric molecular oxygen abundance inferred from twilight 6300 A airglow

When the local solar zenith angle, χ_L, is < 105° the 6300 A line is much stronger than expected on the basis of F region ionic recombination alone. Between 95 and 105° the additional intensity is quantitatively explained by production of O(¹D) from photolysis of O₂ in the Schumann-Runge continuum, (λλ 1300–1750 A) using current values for solar flux, atmospheric composition and quenching of O(¹D) by N₂. The Schumann-Runge (SR) component exhibits a large seasonal variation with a maximum in summer. We interpret this variation as implying a seasonal change in thermospheric O₂ abundance; the change seems largely to reflect a variation in O₂ density at the base of the diffusive regime although some contribution may come from changes in thermospheric temperature structure. Large changes in the SR component exist from day to day and with a 27 day period following a major magnetic storm. The photodissociation source becomes inadequate when x_l < 95°; at 90° more than half of the intensity comes from still another source which we identify as local photoelectron excitation of O atoms.     

A spectroscopic orbit for the two—Spectrum eclipsing binary RT Persei

Intensified Reticon spectra have been obtained at a high dispersion for the Algol system, RT Persei. They were measured by the cross-correlation technique. The spectroscopic elements, revised for the primary component and determined for the secondary for the first time, are: T₀ = HJD 2,446,038.9332, K₁ = 55.0, K₂ = 194.7, V₀ = −8.3 km/s. A mass ratio q = m₂/m₁ = 0.282 is deduced. A circular orbit is adopted. The spectrum of the primary is F5V, and the secondary is a subgiant. With the elements determined here and the published photometric parameters, the absolute dimensions of the binary are: A = 4.20, R₁ = 1.20, R₂ = 1.08 R; M₁ = 1.08, M₂ = 0.30 M.     

Properties of the infrared dark cloud G79.2+0.38

The MSX infrared dark cloud G79.2+0.38 has been observed over a 11′×′ region simultaneously in the J=1-0 rotational transition lines of the ¹²CO and its isotopic molecules ¹³CO and ¹⁸CO. The dense molecular cores defined by the C¹⁸O line are found to be associated with the two high-extinction patches shown in the MSX A-band image. The two dense cores have the column density N (H₂) (5 – 12) × 10²² cm⁻² and the mean number density n (3 ± 1) × 10⁴ cm⁻³. Their sizes are 1.7 and 1.2 pc in ¹³CO(1-0) line, 1.2 and 0.6 pc in C¹⁸O(1-0) line, respectively. The masses of these cloud cores are estimated to be in the range from 2 × 10² to 2 × 10³ M. The profile of radial mean density of the cloud core can be described by the exponential function ¯n(p) p^{−0.34±0.02}. Compared with the cases of typical optical dark clouds, the abundances of the CO isotopic molecules ¹³CO and C¹⁸O in this MSX infrared dark cloud appear to be depleted by a factor of 4–11, but at present there is no evidence for any obvious variation of the relative abundance ratio X_13/18 between ¹³CO and C¹⁸O with the column density.     

Density profiles of dark matter halos with anisotropic velocity tensors

We present density profiles, that are solutions of the spherical Jeans equation, derived under the following two assumptions: (i) the coarse grained phase-density follows a power-law of radius, ρ/σ³ ∝ r⁻, and (ii) the velocity anisotropy parameter is given by the relation β_a(r)=β₁+2β₂ (r/r_*)/[1+(r/r_*)²] where β₁, β₂ are parameters and r_* equals twice the virial radius, r_vir, of the system. These assumptions are well motivated by the results of N-body simulations. Density profiles have increasing logarithmic slopes γ, defined by γ=−d ln ρ/d ln r. The values of γ at r=10^−2.5r_vir, a distance where the systems could be resolved by large N-body simulations, lie in the range 1.0–1.6. These inner values of γ increase for increasing β₁ and for increasing concentration of the system. On the other hand, slopes at r=r_vir lie in the range 2.42–3.82. A model density profile that fits well the results at radial distances between 10⁻³r_vir and r_vir and connects kinematic and structural characteristics of spherical systems is described.     

Supernova remnants and the spiral structure of the Galaxy

A set of unit clouds of 10⁴ M randomly distributed between 3 and 7 kpc radii, move under the general gravitation of the galactic disk and their mutual gravitation. When the clouds collide they form loose aggregates or giant molecular clouds (GMC). Star formation rate is assumed to be proportional to the mass of the GMC. The more massive stars formed soon turn into supernovae, which in turn break up the GMC back into the unit clouds. After some 350 Myr a steady state is reached, in which the GMCs have a mass spectrum of gradient −1.6, and has the mass-radius relation M ∞ R², both in agreement with the observations. From our simulation we find there should be 775 ± 12 supernova remnants in our galaxy. The existence of spiral arms does not increase the production rate of supernova remnants, but it does make the GMCs to concentrate around them.     

Changes in the ionospheric F2-layer at a place near the Sq-current focus during geomagnetic storms

In this paper hourly data of maximum electron density and total electron content in a unit column up to the level of peak electron density of the F2-layer at Puerto Rico (magnetic dip 52.5°N) in the American sector are studied to find their DS and D_st variations and to compare them with those of the horizontal component of the Earth's magnetic field for 93SC type geomagnetic storms which occurred during the period September 1957–March 1962. These variations are obtained separately for positive and negative F2-storms and then averaged for all the types. It is found that the positive F2-storms are in a way connected with the equatorial type of DS variation of the H-field and the negative F2-storms with the high-latitude type DS variation of the H-field. The D_st variation of the H-field is practically of the same character for both positive and negative F2-storms. These findings combined with those of others indicate that it is the DS current in the ionosphere that cause the observed changes in the F2-layer through electromagnetic movements; diffusion along the field lines and changes in the loss-rates of electrons may also contribute to the nett effects. A statistical survey shows that while there are equal chances for positive F2-storms in Summer and Winter at Puerto Rico, there is a much larger number of negative F2-storms in Summer than in Winter. At a southern conjugate place, there is a much larger number of positive F2-storms in Winter, but equal number of negative F2-storms in Summer and Winter. More than half the total number of the F2-storms are found to be similar types (33 per cent positive, 23 per cent negative) from the consideration of the F2-changes during individual magnetic storms at the conjugate places. These are discussed in the concluding section of the paper.     

Long-term Variability Properties of Mkn501

Optical photometric observations at the I and R wavebands were carried out towards Mkn501 using the 1.56 meter optical telescope of Shanghai Astronomical Observatory at Sheshan. Combining our new observations with the published historical data, we have obtained the light curves of Mkn501 at the optical, infrared and radio wavebands with a time coverage of nearly 80 years. The relationship between the light variability and the color index is discussed, it is found that a strong correlation exists between the color indices (B − V) and (B − R), with the correlation coefficient reaching r = 0.73. The correlations of multi-band light variabilities are analyzed by the DCF method, it is found that certain positive correlations of B-band light variability with the 4.8 GHz and infrared light variabilities exist. And the spectral analysis on the B-band light curve with the CLEANest method indicates that the light curve of Mkn501 contains probably two periodical components of (10.06 ± 0.04) yr and (21.60 ± 0.17) yr.     

Short-period fluctuation analysis of the new BIH LOD series

In this paper, we analyse the short-period tidal fluctuations in the new LOD series of ERP (1962.0 – 1982.0) reduced by Li Zhengxin, using the Marple algorithm. The Marple spectral analysis reveals sharp peaks at 13.652, 27.586 and 31.746 days. They are consistent with the tidal terms M_f, M_m and MS_m. Their amplitudes are estimated.

The elastic deformation parameter K/C is calculated at the fortnightly and monthly frequencies. A least squares solution gives 0.56 ± 0.21 and 0.89 ± 0.21 at these two frequencies. The difference between these two values is not significant.     

The embedded cluster DBSB 48 in the nebula Hoffleit 18: Comparison with Trumpler 14

We derive fundamental parameters of the embedded cluster DBSB 48 in the southern nebula Hoffleit 18 and the very young open cluster Trumpler 14, by means of deep JHK_s infrared photometry. We build colour–magnitude and colour–colour diagrams to derive reddening and age, based on main sequence and pre-main sequence distributions. Radial stellar density profiles are used to study cluster structure and guide photometric diagram extractions. Field-star decontamination is applied to uncover the intrinsic cluster sequences in the diagrams. Ages are inferred from K-excess fractions. A prominent pre-main sequence population is present in DBSB 48, and the K-excess fraction f_K = 55 ± 6% gives an age of 1.1 ± 0.5 Myr. A mean reddening of A_Ks=0.9±0.03 was found, corresponding to A_V = 8.2 ± 0.3. The cluster CMD is consistent with the far kinematic distance of 5 kpc for Hoffleit 18. For Trumpler 14 we derived similar parameters as in previous studies in the optical, in particular an age of 1.7 ± 0.7 Myr. The fraction of stars with infrared excess in Trumpler 14 is f_K = 28 ± 4%. Despite the young ages, both clusters are described by a King profile with core radii R_core = 0.46 ± 0.05 pc and R_core = 0.35 ± 0.04 pc, respectively, for DBSB 48 and Trumpler 14. Such cores are smaller than those of typical open clusters. Small cores are probably related to the cluster formation and/or parent molecular cloud fragmentation. In DBSB 48, the magnitude extent of the upper main sequence is ΔK_s ≈ 2 mag, while in Trumpler 14 it is ΔK_s ≈ 5 mag, consistent with the estimated ages.