High resolution spectroscopy of the disk chromosphere

We describe time-series observations of small-scale Ca ii emission features located outside the network in the quiet chromosphere. Simultaneous spectra in K and λ 8542 show unambiguously that the evolutionary behaviour of the K-line profile due to an outwardly propagating velocity pulse. Assuming that this pulse is a progressive acoustic wave, as suggested by the inferred flow parameters, we show that the wave loses mechanical energy in traversing the chromosphere. This implies that the bright Ca ii features (K-grains) are the manifestation of local heating in the chromosphere, possibly by shock waves.

     

High resolution spectroscopy of the disk chromosphere

We describe the properties of dark structures which are seen in the K-line wings and which seem to propagate inward into the K-line core, or upward in the solar atmosphere. These so-called dark whiskers appear to be related to the bright disturbances (bright whiskers) described by Liu (1974). Both may be related to the shocks that heat the chromosphere and corona.     

High resolution spectroscopy of the disk chromosphere

Two independent sets of high resolution time series spectra of the CaII H and K emission obtained at the Solar Tower and at the Big Dome of the Sacramento Peak Observatory on September 11th, 1971 are reported. The evolutionary behaviour of the emission first reported by Wilson and Evans is confirmed but the detail of the evolution is found to be more complex. In one case, a doubly peaked feature showing some K₃ emission evolves into a single K₂ (red) peak with no K₃ emission. Coincidentally, a neighbouring doubly peaked feature evolves to a very strong blue peak. In an entirely independent sequence a doubly peaked feature evolves into a single red peak. The K₂ emission then fades completely although the continuum threads are still strong. Finally a strong K₂ blue peak appears. These developments are confirmed by intensity profiles obtained from the spectra.Image motion during the sequences is measured using slit-jaw photographs and changes in the overall pattern of the spectra. It is found to be less than the size of the individual features, i.e. 1–2.While considering that the evolution can be explained by the relative motion of one feature with respect to another during the sequence, it is shown that it is possible to account for all these examples in this way only by invoking coincidence of a very high order.It is concluded that in these cases the observed evolution of the K₂ emission is due to temporal variations in the physical conditions which give rise to them.     

High resolution observations of the chromosphere at mm and cm wavelengths

High resolution observations of the Sun at 3.3 mm, 3.5 mm, 1.35 cm, and 1.95 cm which were obtained by tracking narrow beam width antennas on the lunar limb as it occulted the Sun are described. The observations indicate that: (1) the region emitting at these wavelengths is very irregular with typical length scales smaller than one half minute of arc, (2) the number of roughness elements responsible for the irregular structure is small within an area of one half minute of arc square, and (3) the roughness elements observed at wavelengths greater than 1 cm extend to 10⁹ cm beyond the optical limb.     

High resolution spectroscopy with CSHELL

CSHELL, the NASA Infrared Telescope Facility Cryogenic Echelle Spectrograph was designed to fill a need for high sensitivity, high resolution, long slit near-infrared spectroscopy. Scientific programs in the areas of comets, planetary atmospheres, young stellar objects, the interstellar medium, and galactic dynamics have been pursued with CSHELL and are described herein. The future of the instrument is also discussed.     

The bright streaks in the Hα disk chromosphere

Evidence is presented demonstrating the existence of a type of chromospheric structure in the form of bright streaks. These are extensions across the solar disk of elongated bright mottles which originate in the central regions of clusters of mottles. They are best observed on good filtergrams at H ± 0.5 Å through comparison with filtergrams at other positions on the line profile. Their length can be as much as 200 sec of arc. The bright streaks appear to be predominantly horizontal loop structures, while the well-known spicules are mainly vertical structures. A bright streak may be well defined or rather diffuse along its length, and many of them are accompanied by darker boundaries or envelopes. It is usual to find a loop of bright streak bridging the central areas of two mottle clusters. It seems that the observed pattern in the space between the chromospheric network at H ± 0.5 Å results partly from the interactions of the bright streaks of different stages of evolution traversing the area in different directions.     

High resolution spectroscopy of solar activity

We describe an observing program designed to obtain high spatial resolution photographic spectra of solar active region phenomena, with time resolution as short as 6 s. The Vacuum Tower Telescope and Echelle Spectrograph at Sacramento Peak Observatory are used to make observations simultaneously in H, He D₃, Ca ii K, Mg b₁, the CN bandhead at 3883, and the magnetically-sensitive line Fe i 6302. Images reflected from the slit jaw are exposed simultaneously in white-light and H. Observations of chromospheric heating, following a high-velocity infall along an H superpenumbral filament, are presented to illustrate the capabilities of the program.Operated by the Association of Universities for Research in Astronomy, Inc., under contract AST 78-17292 with the National Science Foundation.     

High resolution spectroscopy of the semi-regular variable LR Sco

A detailed spectroscopic investigation of LR Sco which was earlier misclassified as R CrB star is made. Atmospheric parameters and elemental abundances are determined using detailed depth-dependent model atmospheres and line synthesis technique. Most of the elements show near solar abundances. The strength of circumstellar components seen in Na D lines are used to derive the mass loss rate. Another independent estimate of mass loss rate is made using the observed infrared flux from 1–100Μm. These two approaches lead to nearly the same value of mass loss rate whenM _vis assumed to be – 4.5 for this star.     

High resolution stellar spectroscopy with VBT echelle spectrometer

The optical design and performance of the recently commissioned fiber fed echelle spectrometer of 2.34 meter Vainu Bappu Telescope are described. The use of it for stellar spectroscopic studies is discussed.     

High spatial resolution spectroscopy of Tycho's SNR with Chandra

We present high spatial resolution X-ray spectroscopy of Tycho's supernova remnant(SNR)using observational data from Chandra. The whole remnant was divided into 26 × 27 regions, with each of them covering 20′′× 20′′. We selected 536 pixels with enough events to generate spectra and fit them with an absorbed two component non-equilibrium ionization model. We obtained maps of absorbing column density, weight-averaged temperature, ionization age and abundances for O, Ne, Mg, Si, S and Fe, with emission used to determine the weight. The abundance maps and the finding that Fe abundance is not correlated with any other element suggest that Fe is located at a smaller radius than other elements,supporting the onion shell model with emission from more massive elements peaking more toward the center. A tight correlation between Si and S abundances support both Si and S coming from explosive O-burning and/or incomplete Si-burning. O and Ne abundances show no correlation with any other element. Considering that O, Ne and Mg are all synthesized in the same process(C/Ne-burning), we suggest that O/Ne/Mg might mix well with other elements during the explosion of the supernova and the expansion of the SNR.     

High resolution spectroscopy of R Coronae Borealis during the 1988— 1989 minimum

Moderate-resolution spectra of the C₂ Swan 0-1 bandhead, the Na I D lines and the K_I resonance lines near 7660 Å obtained at minimum light during the 1988–1989 decline of R CrB are discussed and interpreted in terms of a popular model for R CrB declines. High-resolution spectra obtained at maximum light show blue-shifted chromospheric emission in the cores of the Na I D and the Sc π 4246.8 Å lines     

High spatial resolution spectroscopy of G292.0+1.8 with Chandra

We present high spatial resolution X-ray spectroscopy of supernova remnant G292.0+1.8 made with Chandra observations.The X-ray emitting region of this remnant was divided into 25×25 pixels with a scale of 20 " ×20" each.Spectra of328 pixels were created and fitted with an absorbed one component non-equilibrium ionization model.With the spectral analysis results,we obtained maps of absorbing column density,temperature,ionization age and abundances for O,Ne,Mg,Si,S and Fe.The abundances of O,Ne and Mg show tight correlations between each other in the range of about two orders of magnitude,suggesting that they are all from explosive C/Ne burning.Meanwhile,the abundances of Si and S are also well correlated,indicating that they are the ashes of explosive O-burning or incomplete Si-burning.The Fe emission lines are not prominent in the whole remnant,and their abundance is significantly reduced,indicating that the reverse shock may not have propagated to the Fe-rich ejecta.Based on relative abundances of O,Ne,Mg,Si and Fe to Si,we suggest a progenitor mass of 25- 30 M_⊙ for this remnant.     

Spectroscopic investigation of the chromosphere

The cloud model employed in the analysis of chromospheric contrast profiles is subject to two criticisms. The source function in the cloud may not be varied independently of the Doppler width in the case of Hα and the radiative coupling between the cloud and the underlying atmosphere cannot be ignored. These criticisms are investigated quantitatively with two simple extreme models. It is found that by taking account of both effects the cloud model may be reinstated. Observed chromospheric features may be understood in terms of clouds of varying parameters embedded in the uppermost regions of a generally undisturbed homogeneous atmosphere. The variable cloud parameters are the optical thickness, the Doppler width, the bulk velocity and the angular size viewed from the line forming regions of the underlying atmosphere. Without multidimensional models the distribution of these parameters in chromospheric features observed at supergranulation boundaries for instance cannot be determined. General considerations however allow the interpretation of plagettes as simply low-lying mottles and allow the chromospheric velocity distribution derived by the original cloud model analysis to be upheld.     

The mystery of the chromosphere

We discuss many aspects of the solar chromosphere from an observational point of view, and show that most existing models are in direct contradiction to radio and eclipse measurements. We plead for attention to the actual observed radio temperatures and density gradients, as well as images of the chromosphere. We find that the chromosphere is not in hydrostatic equilibrium and suggest that the support is due to the tangled intranetwork fields.Dedicated to Cornelis de Jager     

High resolution spectroscopy of two young active late type stars within 20 parsecs of the Sun

We present high-resolution optical echell spectroscopy of HIP 544 and HIP 46843, two nearby solar like stars. The discovery of these young stars at such a close distance to the Sun is really a surprising phenomenon. It will help us to have a better understanding of the structure and evolutionary history of the Milky Way. The radial ve-locities (RV) of HIP 544 and HIP 46843 are measured to be -6.88±0.13km s-1 and 8.30±0.16km s-1, respectively, which are more accurate than before. The equivalent widths (EW) of the Li I 6707.8 A absorption line of HIP 544 and HIP 46843 are mea-sured to be 110±5mA and 195±5mA respectively. Based on these properties, HIP 544 is estimated to be 100-800Myr old and HIP 46843 30-100Myr old using three relatively creditable methods.     

High resolution spectroscopy in the far UV: Observations of the interstellar medium by IMAPS on ORFEUS-SPAS

The Interstellar Medium Absorption Profile Spectrograph (IMAPS) is an objectivegrating, echelle spectrograph built to observe the spectra of bright, hot stars over the spectral region 950–1150Å, below the wavelength coverage of HST. This instrument has a high wavelength resolving power, making it especially well suited for studies of interstellar absorption lines. Following a series of sounding rocket flights in the 1980's, IMAPS flew on its first Shuttle-launched orbital mission in September 1993, as a partner in the ORFEUS-SPAS program sponsored by the US and German Space Agencies, NASA and DARA.On ORFEUS-SPAS, IMAPS spent one day of orbital time observing the spectra of 10 O- and early B-type stars. In addition to outlining how IMAPS works, we document some special problems that had an influence on the data, and we explain the specific steps in data reduction that were employed to overcome them. This discussion serves as a basic source of information for people who may use archival data from this flight, as well as those who are interested in some specific properties of the data that will be presented in forthcoming research papers.IMAPS is scheduled to fly once again on ORFEUS-SPAS in late 1996. On this flight, 50% of the observing time available for IMAPS and two other spectrographs on the mission will be available to guest observers.     

Oscillations of the upper chromosphere

Variations of intensity and wavelength in several UV lines have been observed with the SUMER spectroheliometer onboard SOHO, and they have been analysed to obtain oscillation spectra and phase differences between lines of different ions. Lines intensities of neutral or singly ionized atoms (with temperature of formation 30000 K) exhibit an increase of oscillatory power between 2.5 and 7 mHz, which may be considered as the signature of p modes. Lines of highly ionized elements (with a temperature of formation 50000 K) yield power spectra which are continuously decreasing with frequency. Brightness variations of the continuum at different wavelengths between 1000 and 1400 Å present oscillations in the same frequency range. Thus, p modes seem to be efficiently stopped by the transition region. No clear evidence is found for the existence of a chromospheric oscillation mode. Phase comparisons between lines formed at different altitudes (in particular Sii and Siii) indicate that these lines oscillate in phase, within the precision of the measurements.     

Spectral investigation of the chromosphere

The results of the analysis of 16 H spectra taken with high spatial resolution are presented. The properties of the line profile in the boundary regions of supergranular cells (SGB) are described by the statistical distribution functions and correlation coefficients of four parameters which determine the shape of a suitable fitting curve. Although some of the line profile properties of both H and H in the SGB can be interpreted in terms of a model which was recently proposed by Durrant (1975) the agreement between that theory and our observations is not entirely satisfactory.Mitteilungen aus dem Fraunhofer Institut Nr. 137.     

Spectral investigation of the chromosphere

Highly resolved H spectra and filtergrams obtained at the Fraunhofer Observatory on Capri were analysed by a method whose principles have been described before. As a result the tentative conclusion of our previous work has been confirmed: The mottles of the chromospheric fine structure are clouds superimposed on the low chromosphere. Furthermore, it is proposed that the latter is identical with the interior of the supergranular cells whose spatial averages lend themselves to an interpretation in terms of a spherically symmetric model. On the other hand, we present evidence that the boundary regions which are formed by the mottles of the fine structure pattern and which constitute the upper chromosphere are not adequately described by spatial averages. Instead, the properties of the individual structural elements should be taken into account by an appropriate theory, if only in a statistical fashion. Some of these properties, viz. source function, optical thickness, Doppler width and velocity, were measured for a large number of elements. On the basis of indirect evidence we suggest that the spicules seen on limb photographs of chromospheric lines are identical with the elements of the supergranule boundary structure.Mitteilung aus dem Fraunhofer Institut Nr. 116.