We present surface maps of the RS CVn system UX Ari. One of the goals of our observing campaign is to monitor long term magnetic activity on this system. To achieve this, we need long time series of observations. The spectral observations described here were obtained in two seasons, December 1995 and November 1996, using the NOT and the SOFIN spectrograph. The NOT with its excellent image quality and SOFIN with its extremely high spectral resolution are well suited for observations of this kind. Due to unfavourable weather conditions only five out of the planned ten spectra were obtained in 1995. This led to incomplete rotational phase coverage, but it was still possible to obtain a stellar surface map for this season. The ten spectra obtained in 1996 cover more than one complete stellar rotation. The data reduction was performed using software especially developed for SOFIN observations. The resulting stellar surface maps do not show large polar spots as previously found on this system by others. The existence of polar spots is a controversial issue due to the sensitivity of the Doppler imaging technique to stationary perturbations in the spectral line cores. Further, one of the spots seen in 1995 is also visible on the 1996 map, suggesting that spots can have lifetimes of at least one year.
I present results from a search for post-common envelope and pre-cataclysmic variables among well-defined samples of composite spectrum binaries and UV excess objects. The observations include adaptive optics imaging and time-resolved spectroscopy. The results will provide input to and verification of population models and hydrodynamical calculations of common envelope evolution.
The basic assets of a telescope are aperture, field, delivered spatial resolution, wavelength range, quality and ingenuity of instrumentation, size and efficiency of detectors, accessibility, and possibly geography (hemisphere). The competitive edge of NOT now and in the near future is based on its ability to excel in at least two of these areas. In the first years of the next century, the new class of high-performance 8 m telescopes in both hemispheres will greatly outperform NOT in most or all of these respects, except possibly instrumentation. Finding competitive niches for NOT at that time will require very careful and imaginative choices of science goals and instrumentation, and perhaps also fundamental changes in the way NOT is scheduled and operated. Creative forward thinking needs to start soon (=now).
Among its users, the NOT is well known for very good seeing. The present status of the telescope with respect to seeing, and the prospects for improving it to deliver even sharper images will first be discussed, followed by a presentation of the tip/tilt correcting camera HiRAC-I and the plans for the more advanced adaptive optics system HiRAC-II, which will deliver diffraction limited images when used together with the IR camera NOTCam. The talk will be concluded with a discussion how a 2.5 m telescope may compete with and complement the large 8 m telescopes coming on-line these years.
A wide field focal reducer and camera is being built for the NOT. A Schmidt type focal reducer, utilizing an off-axis reflective corrector plate, reduces the effective focal ratio of the telescope from 11 to 4.8 over a field of view of 17.5'×17.5'. The use of a reflective system minimizes problems with ghost images. The detector consists of a 2 by 2 mosaic of 2k×2k 1.5 µm pixel thinned Loral CCD's, giving a scale of 0.25"/pixel. The CCD mosaic may also be used for direct imaging, giving a field of view of 7.5'×7.5' and a scale of 0.11"/pixel.
For the last 2 years we have been actively designing and constructing a near-IR camera/spectrometer for the NOT. This instrument is called NOTCam. In this talk we will consider the design of the instrument, its scientific capabilities in all currently available modes of operation, prospects for using NOTCam in the future, and possible instrument upgrades. We will additionally consider the types of proposals for NOTCam suitable for the commissioning time in September 98.
In the past decade, the surface imaging technique has provided a new opportunity for obtaining detailed temperature images of stellar surfaces. Using high-resolution and high signal-to-noise ratio spectroscopic observations carried out in 1994-1998 with the SOFIN spectrograph installed at the Nordic Optical Telescope, surface images of some active stars have been obtained. The inversion technique applied is the recently developed Occamian approach, which does not put any artificial constraints on the solution and provides an error analysis of the solution. Spot migration, their lifetimes, active longitudes, and activity cycles are discussed for the stars.
Statistically complete samples and detailed observations of nearby galaxies and clusters of galaxies are necessary complements to high redshift studies if we want to understand galaxy formation and evolution. I will review some of the recent NOT observations of the local galaxy population and discuss possible future use and competitiveness of the new core instrumentation with emphasis on what nearby galaxies can tell us about the early stages in their evolution.
Maria Marcha,
University of Lisbon
Antonis Politadis,
Onsala Space Observatory
High resolution images are usually best obtained with the Hubble Space Telescope. However, high spatial resolution can also be achieved with ground based telescopes, by deconvolution of high S/N data obtained under good seeing conditions. Such performance requires good sampling of the data as well as an exceptional PSF stability over the field of view. The small pixel size and the stable PSF of the HIRAC at the NOT, in addition to the excellent optical quality of the telescope make NOT-data perfect for applying the MCS deconvolution algorithm. In the framework of a systematic study of lensed quasars, a field where high angular resolution is crucial, the MCS code has been applied to recent NOT+HIRAC data. We present a summary of the results obtained so far.
IACUB is an un-crossed echelle spectrograph built in a collaboration between the Instituto de Astrofisica de Canarias and the Queen's University of Belfast. The spectrograph is designed as to work within 3100 and 11000 Angstrom, with a spectral resolution up to 50000. Using a narrowband filter as order separator, the wavelength range selected in each observation is limited to a single spectral order, and corresponds to less than 20 Ang in the extreme blue and to 60 Ang in the near-IR. On the other hand, a relatively long slit (45 arcsec) can be used for spatially resolved studies of extended objects.
Owing to its technical characteristics, IACUB is especially suited for observations of stellar and interstellar lines (in particular in the near-UV region which is usually not accessible with the other spectrographs available at the ORM), as well as for kinematical studies of emission-line objects, such as planetary nebulae and active galaxies, at high spectral and spatial resolutions.
IACUB is presently offered as a common user instrument for the NOT within the Spanish observing time: 27 observing runs have been allocated to date.
Hugo E. Schwarz,
NOT
Symbiotic stars are long period, interacting binary systems in which a compact hot star (usually a white dwarf) ionizes part of the wind of a red giant companion. Mass accretion onto the hot component of these systems results in nova-like outbursts during which episodic mass ejections, jet formation, and fast winds from the hot star are often observed. These mass outflows and their dynamical interaction with the red giant's wind have been observed at various wavelengths (from the radio to the X ray domain), and at various spatial scales.
We present some results of a campaign conducted at the NOT aimed at detecting and studying ionized extended nebulae (0.1 to 2 parsec) around symbiotic stars. Three nebulae were discovered in the recent years, and some others are periodically monitored in order to detect structural or illumination changes, and proper motions.
The illustrative case of CH Cyg is presented, and the possible link with bipolar planetary nebulae is discussed.
We present results from a weak lensing study of X-ray luminous galaxy clusters with the NOT. The dark matter distribution in the clusters is found to closely trace the distribution of X-ray gas and luminous galaxies in the clusters. The mass-to-light ratios indicate that O0 = 0.3, i.e. the matter density in the universe falls far short of the closure density O = 1. A completely different constraint on O0 comes from constraining the cluster mass function at z=0.3.
We will also present results from followup cluster observations with the University of Hawaii 8k mosaic CCD, and briefly highlight some of the current methodology for weak lensing analysis of wide-field CCD mosaic data which will be relevant for the future NOT CCD mosaic.
Isotope shifts in spectral lines of Pt and Hg have been studied with the SOFIN high-resolution echelle spectrograph (R=170000) at the NOT and with the Goddard High-Resolution Spectrograph (GHRS) echelle mode (R=85000) on the Hubble Space Telescope (HST). Our target star, HR 7775, is a slowly rotating (v sin i = 2 km/s) HgMn star with exceptionally strong Hg and Pt lines and is thus highly suitable for observing isotopic composition in these elements. The line strengths can be interpreted as enhancements in the abundances of Pt and Hg by factors of 105 and 5×104, respectively, relative to the solar-system material. By applying a synthetic spectrum fitting technique the observed Hg lines can not be fitted with the same isotope mixture. The Hg II l1942 resonance line is best fitted with an isotope mixture of 10:90 for the isotopes 202:204, while the Hg II l3984 line has a best fit with a mixture of 40:60 for 202:204. The Pt lines in the optical region have been fitted with an isotope mixture of 10:60:30 for the isotopes 195:196:198, while an unfortunate effect of coincident wavelengths between some of the isotopes for the UV lines means that the isotope mixture cannot be uniquely determined. The UV lines of Pt and Hg result from transitions between low-lying energy levels, while the optical lines originate from transitions beween somewhat higher energy levels. Since lines originating from different excitation levels may be predominately formed at different heights in the atmosphere the variation in isotope mixture between the UV and optical lines might be reflecting a diffusion process in the star. Additional observations of lines at various excitation states in these elements are being sought to solidify the current findings and further test the diffusion hypothesis. The analysis of the optical Hg lines includes new laboratory wavelength measurements obtained with the Lund Fourier Transform Spectrometer (FTS).
This optical-near-IR survey covers 850 arcmin2 in the central part of the Pleiades open cluster to a limiting magnitude corresponding to ~ 0.035 Mo at the Pleiades age, distance and metallicity.
Nine new possible Pleiades members were discovered, four of which are below the brown dwarf limit. At I=20.55 and I-J=3.40 the faintest candidate has an estimated mass of 0.040 Mo. Since it also shows Ha in emission it is most likely a Pleiades member and thereby the lowest mass brown dwarf identified in the Pleiades at present. Low-resolution spectra of the four brown dwarf candidates and a few brighter cluster members will be presented. The implications of this survey on the mass function for brown dwarfs and their possible contribution to the dark matter will be discussed.
A high resolution, high efficiency spectrograph has been developed for the NOT, mainly financed by the danish VELUX foundation. The spectrograph is fiber fed with a possibility for using a red or blue fiber. The resolution is of the order 50,000 with a wide wavelength coverage.
The instrument now exists as a laboratory model, which is undergoing various tests. Results will be presented. If tests show the instrument to perform according to specifications, we suggest the instrument is installed at the NOT as a standby instrument. A plan and a budget has been worked out for this operation.
Palle Møller,
ESO, Garching;
Bjarne Thomsen,
Institute for Physiscs and Astronomy, Aarhus
In this poster we present results from our search for emission from damped Ly-alpha absorbers (DLAs) at high redshifts. DLAs are representative progenitors of present day galaxies in the sence that all baryons that reside in the galaxies we know today once were cold gas in DLAs. Much information about the evolution of metallicity of DLAs has been collected from the study of QSO absorption lines, but the sizes, morphologies, state of starformation and emission properties of these young galaxies are still largely unknown today. We present some early results about these important qualities of DLAs.
Interstellar clouds show a variety of forms on a large range of size scales. Complexes are composed of ensembles of cloudlets and filaments. We are concerned with the formation and physics of elongated molecular filaments with wavy, sinusoidal shapes. In particular we investigate to what extent magnetic fields can confine the filaments and the possible role of electric currents in the clouds.
We present NOT images of small-scale, helical structures in an elephant trunk in the Rosette nebula suggesting the presence of helical magnetic fields. These imply the presence of electric currents in the trunk.
Elongated dust grains in molecular clouds are subject to magnetic forces which tend to align the spin axis of the grains, and this effect is expected to lead to linear polarization of the light from background stars. We also present the results of an extensive and deep mapping of the linear polarization of stars in three regions with molecular filaments. The observations were made with the CCD polarimeter at NOT, and show that the dark filaments add very little to the background polarization of stars in the areas. This result is in line with what have been found by others from observations of other cloud regions.
We have modeled the effects of polarization in dense interstellar filaments, and these results are discussed in connection with the above-mentioned results.
We present results from Strömgren uvbyß observations of open and globular clusters. These observations can reveal striking new features in the cluster color-magnitude diagrams as well as provide estimates of the cluster reddening, metallicity and distance. Using these parameters we estimate the ages of M5, the famous second parameter pair M3/M13 and M92. We also illustrate how the c1 index can be used to trace abundance anomalies in RGB stars. In the case of M13 we derive an absolute age of 12 Gyr and show that there are now evolved metal-poor field halo stars which are older than this cluster.
The use, until now and in the future, of NOT for studying late stellar evolution is discussed. A number of interesting new possibilities for investigating nucleosynthesis in late stages and structures of photospheres and winds are discussed.
Ilkka Tuominen,
Astronomy Division, University of Oulu
We present surface (Doppler) imaging temperature maps of the FK Comae-type star V1794 Cyg calculated from high resolution spectra taken with the SOFIN spectrograph at the NOT in 1994-1995. The maps show a large cool spot at high latitude (but not the on the pole). Moreover, some evolution in the spot pattern can be seen. The slightly flat bottomed absorption lines of the star would usually be interpreted as caused by a large cool area surrounding the pole (polar cap). We present differential rotation as an alternative way to explain the shape of the line profile.
Recent and more 'mature' results of observations of interacting binaries obtained at the NOT will be presented. The range of objects includes cataclysmic variables (both magnetic and non- magnetic) and X-ray binaries. The presentation mainly concerns photometric and polarimetric studies.
R.M. Stanga,
University of Florence
Radial velocity measurements using the cross-correlation method are discussed and the accuracy of the relative offset determination is derived. The wavelength stability of a high resolution echelle spectrograph mounted at the Cassegrain focus is analysed. A new method is developed, which allows to correct for the change of the positions of the comparison spectrum lines during the scientific exposure by means of a three-dimensional dispersion curve. The 3D-curve is a composition of the individual dispersion curves of several images, where also the effects of the misalignment of the spectral lines with respect to the CCD rows, and optical distortion in the spectrograph are taken into account and considered as a function of time as the spatial orientations of the telescope and the spectrograph change.
The method is used to investigate the instability of the radial velocities of some late-type giants, based on observations with the high resolution echelle spectrograph SOFIN, mounted at the Cassegrain focus of the NOT.
Among the greatest challenges in cosmology today is the understanding of the nature and distribution of dark matter in the Universe. It is well established that dark matter is a non-negligible constituent in all galaxies, but its distribution and quantity remains elusive. We have conducted a survey at the 2.5 m Nordic Optical Telescope to map the dark-matter distribution in field galaxies by obtaining unbiased values for their characteristic (fiducial) velocity dispersions and sizes, accurate to 10 %. To successfully detect the marginal galaxy-galaxy weak lensing effects a mosaiced field of 12'×12' was observed using ALFOSC. Estimated photometric redshifts of the detected galaxies in the field are applied in the lensing analysis to constrain the lensing potential of each lens-source pair. Preliminary results of this analysis are presented.
In order to obtain the initial mass function of young stellar clusters, which are still more or less embedded in their parental molecular clouds, it is of outmost importance, but not trivial, to get a complete sample of the young stellar population. From a mid infrared survey with ISOCAM we have already increased the number of young stellar objects by roughly a factor of 2. In order to sample the faintest population, however, we here consider the method of using variability in the K-band as a criterion of youth and cluster membership. The K-band (2.2 micron) is optimal with respect to sensitivity and extinction, and therefore deep K-band imaging with Arnica at the NOT during several epochs in 1995 and 1996 was obtained for the Serpens Cloud Core. In this poster the first results from these data are presented.
AM Her stars (polars) are binaries where strongly magnetic white dwarf accretes matter from its compagnion. This secondary is a K- or M-class main sequence star. Polars have a very strong magnetic field (in the range of 10 to 100 MG) and due to that and also relatively small separation of the binary components, the formation of an accretion disk around the white dwarf is prevented. The outflowing plasma from the secondary is channeled along the field lines forming accretion columns above the surface of the WD. This hot plasma emit cyclotron radiation in the infrared wavelenghts and it can be observed in the optical region as harmonic overtones. Due to strong magnetic field, light from these objects is polarized (both linear and circular).
We present here observations of several polars (BY Cam, V1309 Ori, V884 Her and QQ Vul) made at NOT with TurPol. TurPol provides an excellent opportunity to study these binary stars in five different spectral bands truly simultaneous and thus provides also possibilities to model the physics in these binary systems very accurately.
Franco Scaltriti,
Turin Observatory;
Harry Lehto, Vilppu Piirola, Tuorla Observatory
The unusually long period (7.98 h) eclipsing polar, RX J0515.6+0105 = V1309 Ori has been target of many optical, infrared and X-ray studies since 1995, when it was identified as a polar. Despite of the large number of optical studies, there has been a need for truly simultaneous multiband polarimetric observations, which are very important in modelling the cyclotron emission on the surface of the magnetic WD. We monitored V1309 Ori between 6 and 8 Oct 1997 with Turpol (UBVRI-photopolarimetry) at the NOT, and in January 1998 at the 2.1 m telescope of CASLEO, Argentina. Due to the epoch of the observations, we were able to observe V1309 Ori about half of the orbital period. Our observations cover the very deep (4 mag) eclipse where the brightness in the U-band fades to 19th magnitude. Circular polarization shows smooth variation between -2 % to +4 %. Linear polarization gives some hints of "the linear polarization pulse" (up to 2-3 %). Our data can be modelled with two cyclotron emission areas (extended arcs) near the opposite magnetic poles of the WD, and the spin axis inclination angle of 80 to 85 degrees. Our simulations also suggest that the magnetic field on the surface of the WD is possibly lower (40-50 MG) what has been assumed in earlier studies of V1309 Ori (55-60 MG).
In this research the Doppler map of the surface temperature distribution on the late type single giant FK Com is presented. The image was derived from high-resolution spectroscopic observations obtained at NOT with SOFIN spectrograph in 1995. The phase coverage and the S/N of these observations are very good. The map was obtained using the spectral region between 6418 and 6435 A. Two cool regions can be seen in the map near the phases 0.25 and 0.6. The region at the phase 0.25 is 900 K cooler and the region at the phase 0.6 is 600 K cooler than the unspotted surface. The spots are situated near the pole, but no real polar caps can be seen. The V and B-V curves were calculated from the map and compared with the quasisimultaneous photometric observations of FK Com. This temperature map can reproduce the observed lightcurves very well. Especially the good fit in the B-V implies that the temperatures in the map are correct. The light curve minimum is at the phase 0.4. This is consistent with the 'flip-flop' phenomenom detected by L. Jetsu. According to the 'flip-flop' the spot activity in FK Com is always consentreted either at phase 0 or 0.5 (when ephemeris 2439252.895 is used).
1) B-I colour maps of the circumnuclear region of several Seyfert 2s (S2) reveal extended blue components aligned with radio and emission line axes. These components probably arise from scattering of nuclear continuum off dust or electrons, in agreement with unified models. 2) Optical/NIR properties of the host galaxies of nearby Seyfert 1s (S1) and S2s are compared. The colours of S2 hosts are similar to those of S1s, but slightly redder than those of spirals, indicating mild extinction and/or reradiation from hot dust. Both Seyfert types show small red colour gradients toward the nucleus, similarly to spirals. Optical S2 host luminosities are similar to spirals, but slightly fainter than those of S1s.
We will present wavelet analysis of UBVRI photometry of AH Her stars.
While progressing in its orbit about the Sun, planet Earth encounters large numbers of small solar system bodies-asteroids, comets, and meteoroids. Occasionally, some of these small bodies collide with the Earth and are destroyed in the atmosphere, while some prevail until a catastrophic impact on the surface. There is vast agreement among scientists that the interplay between the Earth and the small bodies poses a significant, natural hazard for the humankind. It is relevant to work toward preventing the asteroids and comets from colliding with the Earth and, at the same time, toward protecting the humankind from the cosmic impacts. In order to illustrate the significance of potential future astrometry of near-Earth asteroids at the NOT, the close approach to the Earth in year 2028 by the small body 1997 XF11 is analysed by starting from its discovery in 1997 Dec. 6, and gradually adding astrometric observations to the data set. Photopolarimetry of near-Earth asteroids is of utmost importance when characterizing the physical properties of these bodies-a status report is given on the reduction of recent photopolarimetry of asteroids at the NOT.
Johan Fynbo,
University of Aarhus;
Stephen Warren,
Imperial College, London;
Bjarne Thomsen,
University of Aarhus;
Kirsten Knudsen, Leif Hansen,
Copenhagen University Observatory
Recent years have seen an almost explosive expansion in the amount of direct observational data documenting the earliest stages of the epoch of galaxy formation.
Between the CMB fluctuations seen by Cobe, the evolution seen in the number density of absorbing clouds along the line of sight to objects at high redshift, the large number of faint compact galaxies seen in the Hubble Deep Field, and the increase in detail of the N-body-hydro simulations - it appears that many different areas of research are now converging on building a coherent picture of the early universe.
There are, however, still important "Missing Links" which need to be uniquely identified and understood in detail before we can claim that the final picture is indeed coherent and fully understood. One of those "Missing Links" is to understand when and how the major part of the neutral gas in the Universe (which is locked up in cold clouds named "Damped Lyman Alpha cloud" because of the strong damping wings seen in their Lyman Alpha line) starts converting its mass into stars. Another, as of yet, unsolved problem is the question whether early starformation causes creation of large amounts of dust, and what the impact of this dust would be on our observational data.
I shall briefly review the current status of the field, and outline our own lines of attack on the Damped Lyman Alpha (DLA) identification problem and the high redshift dust problem, both of which we are pursuing with the NOT and with the HST.
Spectra between 3100 and 3600 Å are not often obtained, due to limitations set by the atmosphere and by the spectrograph. This particular spectral region is of spectroscopic interest when investigating both hot and cool stars. For the first time spectra were obtained using the SOFIN echelle spectrograph between 3300 and 3600 Å. Two different objects were observed, the sun, investigated by recording reflected light from the moon, and the chemically peculiar star a2 CVn (A0p). The results are compared with each other and some line identifications are presented. The data were obtained with a spectral resolving power of 80000. The SOFIN is capable of a spectral resolution of 170000, which make it possible to investigate bright stars in order to understand the effect of hyperfine structure, isotopic shifts and the Zeeman effect. For high-resolution spectroscopy the NOT/SOFIN is capable to compete with other telescopes, especially when investigating the near-UV spectral region.
An investigation of the magnetic star HR1094 (B9p) has been made with primary interest of the rotational velocity and an abundance analysis of the iron-group elements, Ti, Cr, Fe, Co and the not so common astrophysical element Cl. An effort was made in identifying spectral lines not broadened by mechanisms other than rotation, in order to determine an accurate value of the rotational velocity. The rotational velocity was determined to be less than 17 km/s. Both Co and Cl seems to be overabundant relative to the sun, which is a pattern not shown in many other stars. An investigation into the presence of the rare earth elements yielded, that they are most likely present with both lines from the second and third spectrum. Observations below 3600 Å might remove this uncertainty and an accurate abundance analysis for some of the rare earth element should be possible.
We present a progress report of our ongoing study of a sample of both radio and X-ray bright BL Lacertae objects detected with the ROSAT satellite. About 50 of the 117 objects in the sample have been imaged at the NOT under excellent seeing conditions. We are currently determining the optical morphology of the host galaxies and studying their close environments. Preliminary results are discussed and images of some interesting cases are shown.
The thermal emission from the telescope and the sky starts to be the dominant background emission around 2.3 micrometers and rises steeply with wavelength. Thus, even though the atmosphere has a good transmission in e.g. the 3.4-4 micron and the 8-13 micron regions (L and N windows) it means that the background emission for groundbased observations puts severe constraints on the imaging techniques. Obviously the read-out time has to be shorter than the saturation time (typically a few milliseconds) and in addition the traditional chopping procedure (sky-source-sky-...) has to be applied. Usually the sky chopping is performed by wobbling the secondary mirror. Once these technical problems have been solved we are left with a photon noise limit which certainly excludes the observation of faint visual object without IR excesses. On the other hand, there are phenomena which cannot be studied at shorter wavelengths and a few examples will be given in the present review.
The Nordic Telescope is in three respects not ideal for imaging in the thermal IR:
1. It is too small.
At 10 microns the diffraction limit is 1 arcsecond, while the seeing disc is
slightly smaller than in the visual, i.e. typically 0.5 arcseconds.
2. It has no IR top end (undersized and wobbling secondary). This was a decision taken to lower the cost and simplify the operation. It was however judged that alternative techniques would develope.
3. La Palma is not an ideal site for thermal IR observations. A good site for IR should be cold and dry and in these respects La Palma is not as good as e.g. Mauna Kea (and certainly worse than the South Pole).
Still we are at the Stockholm Observatory spending substantial efforts in developing a mid IR camera for the Nordic Telescope (and in principle the Gallileo and Herschel telescopes). We have in fact a very good scientific reason in our work on the early stellar evolution and the initial mass function (IMF). The present contribution will describe this scientific aspect and the expected performance of the mid IR camera (called SIRCA = Stockholm InfraRed CAmera).
During the last two years, much progress was achieved in the understanding of the Gamma-Ray Burst phenomenon. This was triggered by the first detection of transient X-ray and optical emission after a high-energy event on February 28, 1997. Many ground-based and spaceborne observatories have followed up upon this discovery, and a substantial body of photometric data has been compiled for about ten sources. Distances have been derived for three sources, confirming the widely expected cosmological origin of most events and proving that some Gamma- Ray Bursts belong the most powerful sources in the Universe. Some sources seem to be located in galaxies with high star formation rate, but there is no consensus on the basic energy source, and it may well be that a wide range of models will have to be applied.
Observations from the NOT have been used to identify optical counterpart sources, and characterize their photometric properties and environment.
The facilities and on-going developements for high precision multicolour (simultaneous UBVRI) aperture polarimetry with Turpol, and imaging CCD polarimetry with ALFOSC, are reviewed.
Franco Scaltriti,
Turin Observatory;
George V. Coyne, S.J.,
Vatican Observatory
The structure of circumstellar dust envelopes of Herbig Ae/Be stars has been studied on the basis of high resolution imaging (CCD) polarimetry carried out under excellent seeing conditions (0.4"-0.6" FWHM) at the NOT. The general centrosymmetric pattern of observed polarization vectors is consistent with single scattering by dust particles in the circumstellar envelope, remaining from the protostellar cloud. However, in the dense inner portions, more complex geometries are found for V376 Cas and V633 Cas (LkHa 198). An optically thick disk is resolved around V376 Cas, with the effective radius increasing from approx. 0.8" in the near infrared (approx 1 µm) to approx 1.2" in the optical wavelengths (approx 550 nm). The corresponding linear disk radius is estimated to be 500-750 AU. Evidence is found for a compact unresolved (r < 0.2") disk, possibly a protoplanetary disk, around V633 Cas = LkHa 198.
Paul Smith, Steward Observatory,
University of Arizona;
Sally Laurent-Muehleisen,
IGPP/LLNAL, Livermore;
Wolfgang Brinkmann,
MPIfEP, Garching
We present preliminary results on our programme "Polarimetry of RGB BL LAC objects". Initially the sample was selected by crosscorrelating the ROSAT All Sky Survey and Green Bank 5 Ghz radio survey. In the flux ratio log (Sx/Sr) vs log (So/Sx) diagram this RGB sample fills the gap between radio and X-ray selected BL Lacs. Preliminary results suggest that more than 60 % of the objects have significant (P > 3 %) polarization, up to P=16 %. The results will be discussed in connecting RBL and XBL subsamples and compared to previous polarimetric studies of BL Lacs.
Jochen Heidt,
Landsternwarte Heidelberg
We present results of deep imaging of radio loud BL Lac objects. Our sample consists of the objects in the 1 Jy sample (Stickel et al. 1991, ApJ, 374, 431) observable at the NOT. The aim of the programme is to study the properties of the host galaxies of these BL Lacs and their close environments. This will allow us to test the Unified Scheme of the radio loud Active Galactic Nuclei.
This review talk covers star formation from an observational point of view for low and intermediate mass stars. It goes through the classification scheme for proto-stars, discusses evidence for accretion discs, infall and outflow phenomena like jets, molecular outflows and HH objects.
Since the earliest stages of star formation can only be studied in the radio and sub-mm regime, the talk gives quite a few results from the first sub-mm camera, SCUBA, which has been in operation on JCMT, Hawaii, since June 1997.
The talk also covers optically visible young stars like T Tauri, FU Orionis and Herbig Ae/Be stars and attempts to identify areas where observations with mid-sized optical/IR telescopes like NOT would be extremely desirable.
A brief history is given of "FOSC" type instruments, the present ALFOSC is described and its performance and possible upgrades discussed. It is argued that a new generation of such an instrument, with modern optics can replace several classical momo-mode instruments, giving the same or better performance, and additionally allowing a different, more interactive way of doing observational science.
Our ongoing programmes taking deep images of different types of BL Lac objects with the NOT have continued now more than four years. Altogether we have images of about 100 objects. In all cases we have observations with sub-arcsecond or sometimes even almost sub-half-arcsecond seeing. The main question we are trying to answer is, if interactions or merger processes play an important role in the violent activity observed in these objects.
For some Cataclysmic Variables, the accretion disk is the dominant member of the system, and light modulations obseved can be attributed to variation of the disk structure or the observed aspects of the disk. This is in particular the case for the AM CVn systems, which are interacting binary white dwarf systems with extreme mass ratios between the components. The disk will in many cases expand beyond the tidal radius, and numerical simulations show that 2 armed and 3 armed spiral structures may appear as stationary structures in the disk. Such structures may produce low amplitude periodic modulations of the light curve from the system, and by observing and analysing such ligh curves, one may diagnostic the shape and structure of the accretion disk. The signature of periodic structures may be observed as a series of harmonically related frequencies in the FT of the lightcurve, and this is a new tool to diagnose the shape and structure of such accretion disks.
The first scientific programmes at the NOT were polarimetric and photometric blazar monitoring programs. The main object in these studies have been OJ 287, in which the deepest ever recorded minimum was seen during May 1989. This was the first scientific result obtained at the NOT. One major blazar monitoring program since 1993 has been the OJ-94 project, in which OJ 287 has been observed and its predicted outbursts confirmed. During the last years most of this monitoring has been done within large multifrequency campaigns involving satellite observations. We will review and discuss these and other blazar monitoring studies.
Ilkka Tuominen, Ilya Ilyin,
Astronomy Division, Dept of Physical Sciences, University of Oulu
Extensive observations of stars with a double energy source (helium burning in the centre and hydrogen burning in the shell) were accomplished at the NOT using the high resolution spectrograph SOFIN. The aim of the observations was to obtain the main atmospheric parameters and abundances of more than twenty chemical elements. Abundance anomalies caused by the mixing to the surface of material processed in nuclear reactions inside a star may provide valuable information both on the nuclear reactions in evolved low mass stars and on the mechanisms driving the processed material to the stellar surface. Such abundance anomalies are dependent on the parameters of stellar atmospheres like the effective temperature, surface gravity and overall metallicity. A sample of RHB stars so far investigated was very small, especially the data for metal abundant stars had to be increased. We have observed 9 such stars in the open cluster M67, 14 stars identified in the Upgren's North Galactic Pole Survey of 1962 and 6 stars presented in the lists of Harlan in 1969-1981. In our contribution we will present the results of the analysis.
Francesco Palla, Antonella Natta,
Osservatorio Astrofisico
di Arcetri, Florence
Filippo Mannucci,
CAISMI-CNR, Firenze;
Ruggero Stanga,
Dipartimento di Astronomia e Scienza dello Spazio, Firenze;
Göran Olofsson,
Stockholm Observatory
History, present status, future developments, scientific goals and main results of the high-resolution spectrograph SOFIN are briefly described.
The talk will provide an overview of the current status in this field. New and improved instrumentation is providing icreasingly better possibilities for the study of comets, asteroids and small moons at the outer planets. It seems that a more general picture is emerging of interactions and similarities between the various classes of bodies.
New observations, in particular of recent comets - including Comets Hyakutake and Hale-Bopp - and newly discovered Trans-Neptunian objects have greatly contributed to the current progress. The future availability of medium-class and large ground-based telescopes with state-of-the-art optical and infrared instrumentation promises further important advances within this field of research. Data from space-based facilities complement the ground-based programmes.
The observations include surveys to identify new objects, accurate astrometry to determine their orbits, as well as multi-colour photometry and spectroscopy to study their dynamical state and surface characteristics. Based on these data, theoretical considerations provide insights into evolutionary scenarios.
With its complement of excellent instruments, the 2.5-m NOT is very well suited for participation in these types of programmes. Some particularly promising approaches will be mentioned.