We propose a self-consistent approach of the CP star phenomenon and try to solve simultaneously the problems of abundance spots, wind and X-ray emission from these stars. We also discuss the periodic X-ray emission from the 07V star θ1 Orionis C and its link with Bp stars.

Côté (1995) surveyed the nearby Centaurus A (Cen A) and Sculptor (Sci) group regions in the search for gas-rich, dwarf irregular galaxies (Irr) which are associated with these galaxy aggregates. 36 Irrs have been found and confirmed as new group members via 21cm/Hα redshifts. In finding this large number of Irrs, the question rises whether systems from the other dwarf galaxy family, the gas-poor dwarf ellipticals (dE), also exist in the two groups. So far nothing is known about dE membership but taking into account the morphology-density relation for dwarfs (Binggeli et al. 1990) a number ratio Irr/dE≈ 1 - 2 would be expected. Prompted by these “missing” dEs we started a large program to identify and study dEs in Cen A and Sci. The main scientific goals are (1) to find dE candidates and to establish group membership via velocity or distance and (2) to estimate the luminosity function (LF) of dwarf galaxies to the faintest possible luminosities. For the two groups, being respectively at a mean distance of 4.0 Mpc and 2.5 Mpc, we will be able to reach dwarf galaxies 4-5 magnitudes fainter than in the previous studies in the Virgo and Fornax clusters and the five groups Leo I, Dorado, NGC1400, NGC5044, and Antlia (Sandage et al. 1985, Ferguson &: Sandage 1990). We briefly outline here first results from the CenA group. All details about the complete survey including Scl will be presented in Jerjen et al. (1997)

We have carried out a large area survey for nearby LSB galaxies to try and answer the following questions:

1. 1. How are LSB galaxies distributed relative to the normal HSB galaxies? Do they have the same clustering properties suggesting that they trace the same mass distribution?

2. 2. What are the implications of the clustering properties on galaxy formation scenarios?

3. 3. Can they account for faint blue galaxies at higher redshifts?

4. 4. Is there any difference between the field and cluster LSB galaxies?

2. The Survey

We have devised an automated technique to pick out local LSB galaxies using 65 UKSTU photographic plates corresponding to 2187 sq.°. We have imposed stringent selection criteria in order to minimise the background contamination. Our galaxies have μ0 ≥ 22.5 B mag arcsec-2 α ≥ 3.0 arcseconds and BT ≤ 20.0. Our survey areas are confined to the Fornax Cluster, the NGC1400, Sculptor and Dorado Groups and the fields between them. The survey, which was carried out in three stages over a period of 2 years, has produced detections of 2435 LSB galaxies (32 galaxies per field). We have estimated the background contamination in three ways: first, by a limited redshift sample, secondly, by Ferguson’s (1989) classification on the Fornax plate and finally, by a numerical simulation of background galaxies. The first method produced an estimate of 14 galaxies per field, while the second and the third methods produced the same estimate of 19 galaxies.

Diagnosis of Ap star magnetic fields through spectroscopic methods is a broad topic, which cannot be fully covered within the rather tight limits of this contribution. Accordingly, the latter is devoted to only one particular approach, namely the determination of the mean magnetic field modulus from the observation of resolved magnetically split lines in high-dispersion spectra taken in unpolarized light. This determination is straightforward, mostly approximation free and model independent. The derived quantity, the mean magnetic field modulus, is the line-intensity weighted average over the visible stellar hemisphere of the modulus of the magnetic vector.

The observational quantities commonly used to study the magnetic field of CP stars – the mean field modulus and the mean longitudinal field, as well as the ‘mean asymmetry of the longitudinal field’ and the ‘mean quadratic field’ recently introduced by Mathys (1995a,b) – are based either on the Stokes parameter / or on the Stokes parameter V. However, a complete description of polarized radiation requires the knowledge of the full Stokes vector: in other words, we should expect that useful information is also contained in linear polarization (the Stokes parameters Q and U); or rather we should expect the information contained in (Q, U) and in V to be complementary, since linear and circular polarization are basically related to the transverse and the longitudinal component of the magnetic field, respectively.

Generally the density of the environment is important for the formation and evolution of galaxies: bright elliptical galaxies reside in the centers of galaxy clusters, whereas late type galaxies preferentially populate small groups, filaments or the outskirts of rich clusters of galaxies. Furthermore, fainter galaxies define smaller voids than bright galaxies. Our investigation of void catalogues in the Northern Local Void region shows that large voids are interlaced by systems of faint galaxies dividing them into smaller subvoids (Lindner et al., 1995). This void hierarchy is an important property of the Large Scale Structure in the nearby Universe and can help to solve problems concerning the distribution of dwarf galaxies and BCDGs.

NGC 595 is a giant Hɪɪ region located in the western part of the spiral galaxy M 33. It is the second in importance in this galaxy, after NGC 604. At 0.84 Mpc, HST is able to resolve its stellar content. Malumuth et al. (1996) obtained HST UV, U, B and V images of this region and derived an ionizing luminosity of 5 × 1050 phots-1 and an average reddening EB-V = 0.36±0.28 mag. The stars are mostly concentrated in the central part of the region, where little emission of gas is seen (the ionized gas lies more in a shell around the stars, figure 1a). Wilson & Scoville (1993) showed the molecular gas to be situated in the south-east part of the region, just outside of the bright knot of stars. Viallefond et al. (1986) found a reddening gradient in the north-east/south-west direction by observing the Hi gas, which was confirmed by Malumuth et al. (1996) with stellar photometry.

We obtained ISO images for NGC 595 in the 5.0 to 8.5 μm range. The emission in this spectral range is dominated by the so-called PAH bands. Current interpretation of these has them originating from stochastically heated molecules. Two of these bands are located in the range observed, at 6.2 μm and 7.7 μm. Stochastic heating implies that the in-band flux is directly proportional to the number of photons absorbed by the molecules. For typical HII regions, Cohen et al. (1989) found 0.58 for the I6.2/I7.7 in-band ratio. However many processes, ionization, dehydrogenation, can modify this ratio. Furthermore, an underlying continuum is present though its exact origin is unknown.

This group of metal poor stars were introduced with the identification of an ‘abnormal’ spectrum for λBoõtis in the famous classification survey of Morgan, Keenan & Kellman (1943) based on a blue sensitive photographic emulsion. More stars were discovered with comparable spectra and with other peculiarities, in particular when the available spectral region was extended to the red and beyond the optical region towards the IR and to the UV.

Ever since their discovery, blue compact dwarf (BCD) galaxies have been thought of as excellent candidates for being young galaxies, i.e. systems presently undergoing one of their very first bursts of star formation. This is mainly because BCDs are very metal-deficient, the metallicities of their ionized gas ranging between Zʘ/50 and Zʘ/3, which makes them the least chemically evolved galaxies in the Universe. Other evidence, such as the very high fractional neutral hydrogen gas content and the lack of an evident underlying old stellar population on optical images, also point to the relative youth of some BCDs.

Thuan, Izotov h Lipovetsky (1997) have argued SBS 0335-052 to be a young galaxy on the basis of the following evidence: 1) HST imaging of the BCD shows its underlying extended low surface brightness component to have an irregular and filamentary structure, suggesting that a significant part of the emission (~1/3) comes not from an underlying stellar population, but from ionized gas. Any underlying stellar population must be younger than ~108yr. Propagating star formation occurs in a chain of 6 super-star clusters with ages ranging between 4 and 30 Myr. 2) The underlying component shows unusually blue colors consistent with gaseous emission, in contrast to most BCDs which possess an underlying red component. 3) VLA 21 cm observations show the BCD to be embedded in an extraordinarily large HI cloud with dimensions some 64 × 24 kpc (the typical size of HI envelopes around BCDs is more like a few kpc in each dimension).

Until the rapid oscillations in Przybylski’s star, HD 101065, were discovered by Kurtz in 1978, chemical peculiarity and pulsation were thought to be mutually exclusive. Though the location of the Ap stars in the HR diagram overlaps with that of the Delta Scuti stars, no Ap stars were known to pulsate, and the Delta Scuti type pulsating stars, with a few exceptions, were not claimed to reveal chemical peculiarity. The striking impact of the discovery of the rapid oscillations of Ap stars is that the basic conception of the exclusiveness of the chemical peculiarity and the pulsation was broken. So far, twenty-nine Ap stars have been discovered to be rapidly oscillating Ap (roAp) stars (Kurtz 1997). The observed pulsations of Ap stars are, however, different from those of the Delta Scuti stars in various aspects. The pulsation periods of roAp stars are typically 10.minutes and are much shorter than those of the Delta Scuti stars, which are typically 2 hrs. In some cases, the amplitudes are modulated with the same period and phase as the magnetic strength variation. The amplitudes of some of the roAp stars are very stable, while some others show a fairly short-term variation of a time scale of a day. Some of the roAp stars show a long-term variation of the frequency with a time scale of years.

Let me first remind you of the subject of the present Joint Discussion. It is about spectroscopy with large telescopes. As I have never done any spectroscopic research of my own and I have never observed with a very large telescope, I am certainly the right person to summarize the most recent results in this area.

NGC 4449 is a bright (B = 9.5), nearby (4 Mpc) irregular galaxy with a high surface brightness and strong star-formation activity; for photos see Hunter and Gallagher (1989). Using the Effelsberg 100-meter dish, van Woerden et al. (1975) - and later also Bajają et al. (1994) - found its HI distribution to extend, at the level 2 × 1019 atoms cm-2 over a full degree, or ten times the D25 diameter. Van Woerden et al. also mentioned that the HI velocity gradient in this outer disk was opposite to that measured at Westerbork over the innermost 4 arcminutes.

With the VLA D-array, we have used a mosaic of 3 × 3 pointings to map the HI at resolutions of 1.0’ and 10 kms-1 over a field (FWHM) of 1° diameter (Hunter et al. 1998). The HI distribution (Fig. 1) shows the following features: 1) a bright inner body, centred on the optical galaxy and dominated by an annulus of 5 kpc diameter; 2) a symmetric elliptical - probably highly inclined - disk of 35 × 15 kpc diameter, with strong condensations at its NE and SW ends; 3) a set of narrow streamers, consisting of straight segments making abrupt angles, and containing several bright clouds. The HI mass in the inner body and elliptical disk together is 12 × 10s Mʘ the streamers (about 7 × 108 Mʘ of HI) are surrounded by a diffuse HI distribution, missed by the VLA interferometers but detected by the Effelsberg single-dish.

In recent years, color-magnitude diagrams have revealed that nearby dwarf galaxies have a fascinating variety of star formation histories. The fact that the dwarfs have periods of star formation activity and inactivity raises several questions. How do the properties of the interstellar medium (ISM) in a galaxy affect its star formation rate? Are the interstellar media of dwarf galaxies similar to those in spirals? And what can we learn about dwarf galaxies’ evolution from their gas contents?

With the achievements obtained in the last few years, in particular most recently, I arrived at the following three hypotheses which seem to combine some major problems of ancient Chinese astronomy on a common historical basis.

Recent studies (Puche & Westpfahl 1994, Young & Lo 1996) have shown that the distribution of HI in some extreme low luminosity dwarf irregular galaxies (e.g. M81dwA, Holmberg I, Leo A) tends to have a ring-like (or shell-like) distribution which suggests that a single burst of star formation could expell most of the remaining ISM (or at least a large fraction of it) from the system. In view of this, Puche & Westpfahl (1994) suggested that in dwarf spheroidal galaxies, the HI should be found at large radii since no young stellar population is observed in most of them.

In this talk we will discuss some aspects of the exchange of astronomical knowledge that took place between the Muslim world and China in the thirteenth and fourteenth century. In that period both the eastern part of the Muslim world, consisting of Persia and surrounding countries, and China, ruled by the Yuan Dynasty, were part of the Mongol world empire. In particular in the period between 1260 and 1280, astronomers as well as astronomical books and instruments were exchanged between Persia and China. As a result, extensive descriptions of a Chinese luni-solar calendar can be found in Arabic and Persian astronomical works from the Mongol period, whereas a Chinese text entitled Huihui Li (“Islamic Calendar”) can be seen to be a translation of a typical Islamic astronomical handbook with tables and explanatory text, in Arabic and Persian called zīj. Islamic astronomy had a good name in China because of its accurate prediction of eclipses, and the Huihui li was used parallel with the official Chinese calendar for almost 300 years.

Na๣īr al-Dīn al-Ṭūsī (1201-1274) composed his Tadhkira at Marāgha in 1261 and altered it with his students and produced his “final version” at Baghdad in 1274. The Baghdad version with all its differences from the Marāgha version was published by Ragep [1993]. That the Tadhkira was considered important by astronomers writing in Arabic is amply attested to by the fact that Ragep [1993] can list fourteen commentaries and supercommentaries as well as refer to numerous other derivative texts.

The line flux ratio of the [C II] 158 μm fine-structure (2P3/2 → 2P3/2) emission to CO rotational emission is a probe of the intensity of the interstellar UV radiation in galaxies. The largest values for the [C II]/CO (J = 1-0) line ratios are found in starburst galaxies, none of which, however, show values larger than 6 ×103 (Stacey et al. 1991). The exception ([CII]/CO ≃ 2 × 104) are galaxies of Magellanic type which have low metallicity, an intense interstellar UV field, and irregular morphology (Table 1).

Mochizuki et al. (1994) showed that the two conditions, a low metallicity and an intense UV field are expected to result in the large [C II]/CO ratios in the Magellanic types. These conditions are likely to be common in more massive galaxies as well, but at an early epoch in their evolution. This suggests that bright [C II] emission can be a good indicator of young galaxies. However, the metal-poor galaxies previously observed in the [C II] line were exclusively Magellanic types. Observations of different types of dwarf galaxies are necessary to help us understand the physical conditions in the interstellar medium of low-metallicity systems.

The Local Group contains 37 currently known or probable member galaxies within a radius of 1.8 Mpc (Grebel 1997a). 31 of these galaxies are dwarf galaxies with MB > -17 mag. The most frequent galaxy types are low-mass, gas-poor dwarf spheroidal (dSph) galaxies, which are dominated by old and intermediate-age populations, and more massive, gas-rich dwarf irregular (dIrr) galaxies with recent star formation. DSph galaxies have been found mostly in close vicinity to the large spiral galaxies in the Local Group, while dirr galaxies tend to be more distant and isolated.

Indian astronomy was introduced into China along with the intrusion of Buddhism. This process lasted about one thousand years in the Mediaeval age. For the study of this process, there are a lot of materials in ancient Chinese historic texts, while the Buddhist scriptures in Chinese translation are very important first-hand materials.