The Zeeman effect for weak magnetic fields

The polarization of a normal Zeeman triplet is discussed for the case in which the lifetime of the excited state of the atom is comparable to or shorter than the period of Larmor precession.     

On the pseudo-π- component in sunspot spectra

The visibility, contrast and displacement of the pseudo--component of a Zeeman triplet, explained as due to saturation, is computed for the triplet at 5250 A (Fe i). Examples of the computational results are given (Figures 1–3).Mitteilungen aus dem Fraunhofer Institut Nr. 89.     

On polarimetry in solar active regions

A new modulation procedure for Zeeman polarimeters is described and tested. The azimuth rotation by means of two steady /4-plates, combined with the common EOLM, has several advantages as compared to two-EOLM-polarimeters. The new polarimeter operates with two /4-plates which are alternately passed through the beam in front of the EOLM by means of an electro-mechanical chopper. The exact time of the /4-plate change is monitored by a photoelectric sensor. The obtained signals drive a number of relays by use of an intervening bistable electronic device. These relays allow to cut-off the erroneous Doppler signal mode and they furthermore distribute the U and Q signals into the corresponding lock-in amplifiers. As a first application of the new polarimeter, the linear polarization is measured in a sunspot penumbra. The telescope was first compensated for instrumental linear polarization down to 5 × 10^-4 by means of a tilted glass plate and well as for phase retardation down to 1° by means of a Bowen compensator.     

Imaging Spectropolarimetry of Ti I 2231 nm in a Sunspot

Spectro-polarimetric observations at 2231 nm were made of NOAA 10008 near the west solar limb on 29 June 2002 using the National Solar Observatory McMath–Pierce Telescope at Kitt Peak and the California State University Northridge – National Solar Observatory infrared camera. Scans of spectra in both Stokes I and Stokes V were collected; the intensity spectra were processed to remove strong telluric absorption lines, and the Stokes V umbral spectra were corrected for instrumental polarization. The sunspot temperature is computed using the continuum contrast and umbral temperatures down to about 3700 K are observed. A strong Tii line at 2231.0 nm is used to probe the magnetic and velocity fields in the spot umbra and penumbra. Measurements of the Tii equivalent width versus plasma temperature in the sunspot agree with model predictions. Zeeman splitting measurements of the Stokes I and Stokes V profiles show magnetic fields up to 3300 G in the umbra, and a dependence of the magnetic field on the plasma temperature similar to that which was seen using Fei 1565 nm observations of the same spot two days earlier. The umbral Doppler velocity measurements are averaged in 16 azimuthal bins, and no radial flows are revealed to a limit of ±200 m s^–1. A Stokes V magnetogram shows a reversal of the line-of-sight magnetic component between the limb and disk center sides of the penumbra. Because the Tii line is weak in the penumbra, individual spectra are averaged in azimuthal bins over the entire penumbral radial extent. The averaged Stokes V spectra show a magnetic reversal as a function of sunspot azimuthal angle. The mean penumbral magnetic field as measured with the Stokes V Zeeman component splitting is 1400 G. Several weak spectral lines are observed in the sunspot and the variation of the equivalent width versus temperature for four lines is examined. If these lines are from molecules, it is possible that lines at 2230.67, 2230.77, and 2231.70 nm originate from OH, while the line at 2232.21 nm may originate from CN.     

A photometric study of three star fields in the southern region of M33

The 2 m RCC telescope of the Rozhen National Observatory (Bulgaria) was used to obtain the colour-magnitude and colour-colour diagrams of OB110 and OB112 associations which form the largest star grouping in the southern region of M33. The stars withV andU20.4 andB21 were measured. TheV magnitude, the coloursB - V, U - B and the respective identification charts are given. This allowed to construct the luminosity function of OB110+OB112. The group has an integrated magnitudeM _VT=–11.8 which is by 0 ^m .5 fainter than OB78 (M31). The mean absorption and the foreground were examined as well.     

The concept of limiting magnitude and the performance of the Isaac Newton telescope for prime focus photography

A quantitative definition of limiting magnitude for stellar photographs is proposed, together with a method of measurement employing a Racine prism. Limiting magnitudes inU, B andV for the Isaac Newton telescope at Herstmonceux derived from a total of 72 prime focus photographs are presented and the results correlated with the size of the photographed image. The limiting magnitude for an extrapolated value of the seeing of 1 isB=22^m.0, in good agreement with a value obtained by scaling the limiting magnitudes of the 200 inch telescope.     

Vector magnetic fields in sunspots

Observations of a round, unipolar sunspot in the Zeeman triplet Fe i 6302.5 with the High Altitude Observatory Stokes Polarimeter are used to derive the vector magnetic field in the spot. The behavior of the magnitude, inclination, and azimuth of the field vector B across the spot is discussed. A linear relation is found between the continuum intensity I _c and the field magnitude B. Time series obtained in the umbra show significant power in the magnitude of the field at a period of t 180 s but the other components of the field vector do not display this behavior.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

A generalized theory for line formation in a homogeneous magnetic field

The formation of spectral lines in a homogeneous magnetic field has been studied. A new method for solving the transfer equations for polarized light has been found. Using this method, the Stokes parameters may be derived without any special assumptions regarding the model atmosphere. With the line formed by pure absorption, the expressions for the Stokes parameters may easily be adapted to numerical calculations. In order to illustrate the method, the line profile for the Zeeman triplet 5250 has been calculated using a photospheric model atmosphere.     

The luminosity of red supergiants in the andromeda galaxy

A blink survey of M31 undertaken by means ofB andV plates taken at the 2 m Rozhen observatory telescope gave the possibility to select ten brightest red supergiant candidates. There are a few bright red supergiants in M31 in comparison the LMC, M33, and our Galaxy. They are more frequent in the northern part of M31 where the higher rate of star formation occurs. Our search indicatedM _V –8.0 for the brightest red supergiants. Their occurrence in a galaxy depends not only on luminosity of the latter but also on the rate of star formation in it.     

The Zeeman broadening of high n solar recombination lines

The Zeeman broadening of high n lines is derived. While in areas of the quiet Sun with field strengths of 1 G the upper boundary of the observable frequency region of recombination lines is defined by electron impact broadening, in active regions with field strengths 25 G the Zeeman broadening will shift this boundary to higher frequencies. The frequency region most favourable for observations is derived and the corresponding Doppler, electron impact and Zeeman broadening are discussed. The strengths of the recombination lines obtained in earlier calculations is reduced when one considers besides the Doppler broadening the electron impact and Zeeman broadening also. The frequency region favourable for observations is compared with the atmospheric transparency of the microwave region; it is found that observations require at least high altitude stations or space-based platforms. Details of using the Zeeman broadening of high n recombination lines for mapping (coronal) magnetic fields are given.     

Observational constraints on a ‘hidden’, turbulent magnetic field of the Sun

A search for linear polarization due to the transverse Zeeman effect in quiet regions near the heliographic north pole has been carried out. The aim is to determine new constraints on the properties of the hidden or turbulent magnetic flux of the Sun. As more than 90% of the total flux seen in magnetograms has its source in kG fluxtubes with an average filling factor of less than 1%, the term hidden magnetic flux refers to the field in the remaining 99% of the photospheric volume, which remains undetected in ordinary magnetograms (at available levels of spatial resolution and sensitivity).Simultaneous recordings of the Stokes I, Q, and V profiles of the Fei 5250.22 and 5247.06 Å lines with 5 × 5 sec of arc spatial resolution have been made with the NSO McMath solar telescope. The analysis shows how the observed Stokes Q amplitudes, as well as the Q/V ratio in combination with the 5250/5247 Stokes V line ratio, provide constraints on the field strength and the angular distribution of the field vectors of the hidden magnetic flux. The field has to be tangled with opposite polarities mixed on a subarcsec scale, and the field vectors have to have large inclinations with respect to the vertical direction, with an angular distribution not far from being isotropic in the photosphere. Constraints on the strength of this tangled or turbulent magnetic field have been obtained by previous methods, which are reconsidered in view of their dependence on the assumed angular distribution. An upper limit of 100 G comes from determinations of magnetic line broadening, a lower limit of 10 G from observed Hanle-effect depolarization.In our observations the linear polarization has been recorded with a precision of 10^-4 with good spectral resolution. Further improvements are impeded by the lack of telescopes with large photon collecting areas and small instrumental polarization.     

High-resolution analysis of solar photospheric oscillations

The coherent 5-min photospheric pressure oscillations with spherical harmonic degrees in the range 100 <l< 1000 were directly imaged over the photosphere with the monochromatic solar telescope FPSS at Meudon Observatory. Movie films were obtained with images spatially filtered to select sizes of increasing wave numbers (or l). Areas with ephemeral concentrations of coherent waves evolve in shape and may move horizontally with velocities of several tenths of km s^–1. When a large number of waves are interacting, the maximum vertical velocity V _max of the pulsation reaches around 1000 m s^–1, irrespective of the size. Extrapolation to the ideal case of a single isolated wave gives V _max proportional to size. For the areas of the smallest scale measured (l = 1000), when about 100 waves are interacting, V _max is found to be 260 + 25 m s^–1 at an altitude of 210 km above the reference level ₅₀₀₀ = 1 and increases vertically with a scale height of 750 ± 400 km.     

Surface photometry of theHii regions S254–S257

The surface photometry of S254–S257 has been carried out by means of a wide range image processing technique in the reduction system. The photographic plates in the H+[NII] andV-bands are taken with the Schmidt telescope. Especially, we have obtained the calibrated map of theHii region, superposing two or more plates with different exposure times, and removing the star images. Three kinds of calibrated maps of theHii regions are drawn: (1)E-map in the (H+[NII]+continuum) (2)V-map in the continuum atV-band, (3)(E-V)-map in the (H+[NII]) line emission. The intensity profiles across the nebular centers were also obtained. Based on calibrated maps, the morphological structure and mass distribution of S255 and S257 are discussed. The location of observed nebulae on the (m _H–m _v) diagram, wherem _H andm _v denote the surface brightness, expressed in the magnitude per square arcmin, is shown together with that of some other nebulae. Some arguements on the age sequence of observedHii regions are presented.     

Magnetic fields and Fe I line profiles in the major solar flare on October 28, 2003

Strong (“kilogauss”) small-scale magnetic fields were detected outside a sunspot near the seismic source of the major X17.2/4B solar flare on October 28, 2003. Echelle Zeeman spectrograms of the flare were obtained with the horizontal solar telescope at the Astronomical Observatory of the Taras Shevchenko Kiev National University. Analysis of the Stokes I ± V profiles for the Fe I 5232.9, 5247.1, 5250.2, and 5397.1 Å lines has revealed a number of characteristic spectral features. These are indicative of both background fields with a strength of ≈300 G and small-scale fields with a strength of 1300–3100 G. Evidence for the presence of another small-scale field component of opposite polarity with a strength of 8–10 kG has been found. A redshift (downflow) with a velocity of 1 km s^?1 was observed in the latter component.     

Spectral classification of Be stars

In the course of observations of the LMC with the Glazar space telescope it was found that the star HD 269665 is unusually bright at 1640 A:m ₁₆₄₀ = 5 _. ^m ± 0 _. ^m 1,m ₁₆₄₀ –V = –6 _. ^m 2.     

Results of Magnetic-Field Measurements with the 6-m Telescope. V. Observations in 2011

The paper presents results of measurements of magnetic-field longitudinal components B _e , radial velocities V _r , and projections of the rotation velocity in the line of sight v _e sin i for 74 objects, mainly main-sequence chemically peculiar stars and standard stars. Observations were carried out in 2011 at the 6-m BTA telescope using the Main Stellar Spectrograph (MSS) with a Zeeman analyzer. Seven new magnetic stars were discovered: HD38129, HD47152, HD50341, HD63347, HD188501, HD191287, and HD260858. Three more stars were suspected to have magnetic fields. Observations of magnetic standard stars and non-magnetic stars confirm the absence of any systematic errors capable of introducing distortions into the B _e longitudinal-field measurement results. The paper gives comments on the research results for each of the 74 stars.     

Observations of helium and hydrogen emission in quiescent prominences

Observations of a number of helium triplet ( 10830, 4713, 4471, 3889, 4026) and hydrogen (H, , , ) emission line intensities in six quiescent prominences are presented. The regions of prominence and neighboring corona were raster-scanned by the telescope, and all lines were measured concurrently at each point. The instrumental field of view was 5 × 20. The results are compared with previous observations and theory. In particular, the intensity of the 10830 emission relative to the other triplets is found to differ strongly from the predictions of the recent detailed calculations of Heasley et al. (1974) for model quiescent prominences.     

Interstellar extinction toward the ultradeep Galactic field of the Chandra observatory from 2MASS data

We have measured the interstellar extinction in the region of ultradeep Galactic-field observations by the Chandra telescope (l ^II, b ^II) ≈ 0.1–1.42 using photometric data from the 2MASS infrared allsky survey. The angular resolution of our interstellar extinction map is 1′.8. We show that the interstellar extinction has a minimum, A _V ～ 3.4, near the center of the Chandra field of view and increases to A _V ～ 5.8–6 at the edge of the field of view. In addition, we show that the bulk of the extinction is gained in the Galactic disk and is approximately the same for all bulge stars. Our results will be subsequently used to process the Chandra data and to estimate the properties of the stellar population in this region.     

Uv Line Profiles of Biv from a 10-Ps Krf-Laser-Produced Plasma

We use a KrF laser that generates pulses up to 8 × 10¹⁴ watt/cm² when focused onto a boron nitride target. We measured the line profile of the near UV, n = 0, n = 2 transitions of helium-like boron and we studied the triplet 1s2p³P-1s2s³S at 2825.85 (J = 1), 2821.68 (J = 2) and 2824.57 (J = 0) Å, at various positions from the target surface, in order to correlate details of this profile with the presence of self-generated magnetic fields and/or dynamic turbulence among other processes. We fitted the measured profiles to a 0-D model, that includes, Stark, Doppler, Zeeman and instrumental broadening. The effect of the magnetic field was included using an intermediate field calculations. Preliminary results of these measurements are presented and discussed.     

The Zeeman pattern of magnetic lines and their statistical properties in the Fei solar spectrum

The Zeeman patterns of magnetic lines are characterized by their first, second, and third order moments and a minimal equivalent representation is suggested for each line. The statistical properties of the Zeeman patterns of the Fe i lines in the solar optical spectrum are analyzed in detail and the various patterns are classified in three different types according to the relative position of the -components having larger strength.