Line Of Sight Direction Research Articles

Morphology and kinematics of Lynds 1642

The high latitude translucent molecular cloud L1642 has been mapped in the J=1-0 and J=2-1 transitions of 12CO, 13CO and C18O using the SEST radio telescope. We have analysed the morphology and velocity structure of the cloud using the Positive Matrix Factorization (PMF) method. The results show that L1642 is composed of a main structure at radial velocity 0.2 km/s while the higher velocity components at ~0.5 and 1.0 km/s form an incomplete ring around it, suggesting an expanding shell structure. Fainter emission extends to the north with a still higher velocity of up to 1.6 km/s. Such a velocity structure suggests an elongated morphology in the line of sight direction. The physical properties of the cloud have been investigated assuming LTE conditions, but non-LTE radiative transfer models are also constructed for the 13CO observations. We confirm that L1642 follows an r^-1 density distribution in its outer parts while the distribution is considerably flatter in the core. The cloud is close to virial equilibrium. In an Appendix the PMF results are compared with the view obtained through the analysis of channel maps and by the use of Principal Component Analysis (PCA). Both PMF and PCA present the observations as a linear combination of basic spectral shapes that are extracted from the data. Comparison of the methods shows that the PMF method in particular is able to produce a presentation of the complex velocity that is both compact and easily interpreted.

The Durham/UKST Galaxy Redshift Survey - IV. Redshift-space distortions in the two-point correlation function

We have investigated the redshift space distortions in the optically selected Durham/UKST Galaxy Redshift Survey using the 2-point galaxy correlation function perpendicular and parallel to the observer’s line of sight, �(�,�). We present results for the real space 2-point correlation function, �(r), by inverting the optimally estimated projected correlation function, which is obtained by integration of �(�,�), and find good agreement with other real space estimates. On small, non-linear scales we observe an elongation of the constant �(�,�) contours in the line of sight direction. This is due to the galaxy velocity dispersion and is the common “Finger of God” effect seen in redshift surveys. Our result for the one-dimensional pairwise rms velocity dispersion is 1/2 = 416 ± 36kms 1 which is consistent with those from recent redshift surveys and canonical values, but inconsistent with SCDM or LCDM models. On larger, linear scales we observe a compression of the �(�,�) contours in the line of sight direction. This is due to the infall of galaxies into overdense regions and the Durham/UKST data favours a value of ( 0.6 /b)�0.5, where is the mean mass density of the Universe and b is the linear bias factor which relates the galaxy and mass distributions. Comparison with other optical estimates yield consistent results, with the conclusion that the data does not favour an unbiased critical-density universe.

Turbulence in the atmosphere of 31 Cygni.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Turbulence in the atmosphere of 31 Cygni. Spiegel, Edward A. ; Aller, Lawrence H. Abstract We have been attempting to utilize data gathered in the 1951 atmospheric eclipse of 31 Cygni to investigate the hydrodynamics in the atmosphere of the K star. From radial velocities measured during the egress of the 1951 eclipse1 we have calculated correlation coefficients as defined below. The observati9ns here used are velocities at separate points in space-time; hence the correlation coefficients depend on space-time intervals. Moreover, the measured velocities are not velocities at single points in the atmosphere, but are mean velocities along the line of sight, the means being weighted with respect to the contribution of each element of atmosphere to the line intensities. For our purposes, the correlation coefficient is T - ~ v5(t) Vz(t + n) R5 (n) = [~))%52~t) T 52(t + n)i-s' t=n where n is a time interval in days, P is the number of days over which observations are made, t is the index (from I to P), the z direction is the line of sight direction, and v is the observed velocity corrected for orbital motion. The correlation Co- efficient is expressed as a function of n alone, since the transverse velocity of the B star is very nearly constant during the observation period. In this case, n completely specifies the space-time interval on which the correlation depends. If there exists turbulence in the hydrodynamical sense in the giant's atmosphere, moderately large eddies, i.e., those whose characteristic lengths are comparable to half the thickness of the atmosphere, will dominate the observed velocities. Smaller eddies than these will have effects analogous to those of thermal broadening, and larger ones will, if they are much larger than the transverse distance spanned by the observations, alter the observed mean velocities. In terms of this turbulence model, the length scale of the energy-containing eddies can be obtained, if the eddies lie within the detectable range discussed in the preceding paragraph. This is accomplished by replacing n by a corresponding space interval. The space interval is linearly related to n through the transverse velocity of the B star. We have calculated the above correlation for velocities derived from the calcium K line.1 Twenty-two observations, taken over a 3~-day period, were used. The calculated correlation Coefficients imply that, on the basis of this provisional turbulence model, the length scale of the energy-containing eddies is of the order of 2 X I0~ km. I.D. B. McLaughlin, Ap. J. ~~6, 550, 1952. University of Michigan Observatory, Ann Arbor, Mich. Publication: The Astronomical Journal Pub Date: 1953 DOI: 10.1086/106905 Bibcode: 1953AJ.....58Q.229S full text sources ADS |