CTK: A new CCD Camera at the University Observatory Jena

The Cassegrain‐Teleskop‐Kamera (CTK) is a new CCD imager which is operated at the University Observatory Jena since begin of 2006. This article describes the main characteristics of the new camera. The properties of the CCD detector, the CTK image quality, as well as its detection limits for all filters are presented (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Variability of young stars: Determination of rotational periods of weak‐line T Tauri stars in the Cepheus‐Cassiopeia star‐forming region

We report on observation and determination of rotational periods of ten weak‐line T Tauri stars in the Cepheus‐Cassiopeia star‐forming region. Observations were carried out with the Cassegrain‐Teleskop‐Kamera (CTK) at University Observatory Jena between 2007 June and 2008 May. The periods obtained range between 0.49 d and 5.7 d, typical for weak‐line and post T Tauri stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

STK: A new CCD camera at the University Observatory Jena

The Schmidt‐Teleskop‐Kamera (STK) is a new CCD‐imager, which is operated since begin of 2009 at the University Observatory Jena. This article describes the main characteristics of the new camera. The properties of the STK detector, the astrometry and image quality of the STK, as well as its detection limits at the 0.9 m telescope of the University Observatory Jena are presented (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Follow‐up observations of Comet 17P/Holmes after its extreme outburst in brightness end of October 2007

We present follow‐up observations of comet 17/P Holmes after its extreme outburst in brightness, which occurred end of October 2007. We obtained 58 V‐band images of the comet between October 2007 and February 2008, using the Cassegrain‐Teleskop‐Kamera (CTK) at the University Observatory Jena. We present precise astrometry of the comet, which yields its most recent Keplerian orbital elements. Furthermore, we show that the comet's coma expands quite linearly with a velocity of about 1650 km/s between October and December 2007. The photometric monitoring of comet 17/P Holmes shows that its photometric activity level decreased by about 5.9 mag within 105 days after its outburst (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Planetary transit observations at the University Observatory Jena: TrES‐2

We report on observations of several transit events of the transiting planet TrES‐2 obtained with the Cassegrain‐Teleskop‐Kamera at the University Observatory Jena. Between March 2007 and November 2008 ten different transits and almost a complete orbital period were observed. Overall, in 40 nights of observation 4291 exposures (in total 71.52 h of observation) of the TrES‐2 parent star were taken. With the transit timings for TrES‐2 from the 34 events published by the TrES‐network, the Transit Light Curve project and the Exoplanet Transit Database plus our own ten transits, we find that the orbital period is P = (2.470614 ± 0.000001) d, a slight change by ∼0.6 s compared to the previously published period. We present new ephemeris for this transiting planet. Furthermore, we found a second dip after the transit which could either be due to a blended variable star or occultation of a second star or even an additional object in the system. Our observations will be useful for future investigations of timing variations caused by additional perturbing planets and/or stellar spots and/or moons (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cover Picture: Astron. Nachr. 7/2011

Light curve with the flare observed in the Pleiades cluster with the Schmidt‐Teleskop‐Kamera at the University Observatory Jena (see M. Moualla et al., this issue, p. 661).     

Research facilities for solar astronomy at ARIES

The solar observational facilities at ARIES (erstwhile U.P. State Observatory, UPSO), Nainital, began in the sixties with the acquisition of two moderate sized (25 cm, f/66 off-axis Skew Cassegrain and 15 cm, f/15 refractor) telescopes. Both these systems receive sunlight through a 45 cm and 25 cm coelostat respectively. The backend instruments to these systems comprised of a single pass grating spectrograph for spectroscopic study of the Sun and a Bernhard-HalleHα filter, coupled with a Robot recorder camera for solar patrolling inHα respectively. With the advancement in solar observing techniques with high temporal and spatial resolution inHα and other wavelengths, it became inevitable to acquire sophisticated instrumentation for data acquisition. In view of that, the above facilities were upgraded, owing to which the conventional photographic techniques were replaced by the CCD camera systems attached with two 15 cm, f/15 Coude refractor telescopes. These CCD systems include the Peltier cooled CCD camera and photometrics PXL high speed modular CCD camera which provide high temporal and spatial resolution of ∼ 25 ms and ∼ 1.3 arcsec respectively.     

Variable stars in the field of the open cluster NGC 6939

The results of CCD photometric survey performed with the 90/180 cm Schmidt‐Cassegrain Telescope of the Nicolaus Copernicus University Astronomical Observatory in Piwnice (Poland) and the 70/172 cm Schmidt Telescope of the National Astronomical Observatory (NAO) at Rozhen (Bulgaria) of the field of the 1 Gyr old open cluster NGC 6939 are presented. Twenty two variable stars were detected, four of them previously known. Four eclipsing systems (3 detached and 1 contact binary) were found to be members of the cluster. Analysis of the brightness of the contact binary V20 strongly supports the distance to the cluster of 1.74 ± 0.20 kpc. The small population of contact binaries in NGC 6939 confirms also the relatively young age of the cluster. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TAOS – The Taiwanese‐American Occultation Survey

The Taiwanese‐American Occultation Survey (TAOS) seeks to determine the number and size spectrum for small (∼3 km) bodies in the Kuiper Belt. This will be accomplished by searching for the brief occultations of bright stars (R ∼ 14) by these objects. We have designed and built a special purpose photometric monitoring system for this purpose. TAOS comprises four 50 cm telescopes, each equipped with a 2048 × 2048 pixel CCD camera, in a compact array located in the central highlands of Taiwan. TAOS will monitor up to 2 000 stars at 5 Hz. The system went into scientific operation in the autumn of 2005. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Space shuttle observations of terrestrial impact structures using SIR‐C and X‐SAR radars

Abstract— Ten terrestrial impact structures were imaged during two flights of the 1994 space radar laboratory (SRL) experiment. These craters include Wolf Creek, Australia; Roter Kamm, Namibia; Zhamanshin, Kazakhstan; BP and Oasis, Libya; Aorounga, Chad; Amguid, Algeria; and Spider, Connolly Basin and Henbury, Australia. SRL contained two co‐registered instruments; the United States shuttle imaging radar‐C (SIR‐C) polarimetric radar system operating in L‐band (λ = 24 cm) and C‐band (λ = 5.6 cm), and the joint German/Italian synthetic aperture radar (X‐SAR) operating in vertically‐polarized X‐band (λ = 3 cm). Comparisons show SRL images to be complementary to, or in some cases superior to, corresponding optical images for evaluating size, location, and relative age of impact features. Regardless of wavelength or polarization, craters with significant relief appear prominently on radar as a result of slope and roughness effects. In desert regions, longer wavelengths penetrate dry sand mantles to reveal hidden crater dimensions or associated buried landforms. Radar polarities and wavelengths are particularly sensitive to vegetation, surface roughness, and soil moisture or electrical properties. In the more temperate environments of Kazakhstan and Australia, SRL images show detailed stream patterns that reveal the location and structure of otherwise obscured impact features.     

Imaging magnetographs for high‐resolution solar observations in the visible and near‐infrared wavelength region

The Coudé feed of the vacuum telescope (aperture D = 65 cm) at the Big Bear Solar Observatory (BBSO) is currently completely remodelled to accommodate a correlation tracker and a high‐order Adaptive Optics (AO) system. The AO system serves two imaging magnetograph systems located at a new optical laboratory on the observatory's 2^nd floor. The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near‐infrared (NIR) observations in the wavelength region from 1.0 μm to 1.6 μm. The Visible‐light Imaging Magnetograph (VIM) is basically a twin of IRIM for observations in the wavelength range from 550 nm to 700 nm. Both instruments were designed for high spatial and high temporal observations of the solar photosphere and chromosphere. Real‐time data processing is an integral part of the instruments and will enhance BBSO's capabilities in monitoring solar activity and predicting and forecasting space weather.     

The GREGOR Fabry‐Pérot Interferometer

The GREGOR Fabry‐Pérot Interferometer (GFPI) is one of three first‐light instruments of the German 1.5‐meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large‐format, high‐cadence CCD detectors with sophisticated computer hard‐ and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field‐of‐view (FOV) of 50″×38″is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25″×38″. The spectral coverage in the spectroscopic mode extends from 530–860 nm with a theoretical spectral resolution of R ≈250 000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580–660 nm. The combination of fast narrow‐band imaging and post‐factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Front‐ vs. back‐illuminated CCD cameras for photometric surveys: a noise budget analysis

Exoplanetary transit and stellar oscillation surveys require a very high precision photometry. The instrumental noise has therefore to be minimized. First, we perform a semi‐analytical model of different noise sources. We show that the noise due the CCD electrodes can be overcome using a Gaussian PSF (Point Spread Function) of full width half maximum larger than 1.6 pixels. We also find that for a PSF size of a few pixels, the photometric aperture has to be at least 2.5 times larger than the PSF full width half maximum. Then, we compare a front‐ with a back‐illuminated CCD through a Monte‐Carlo simulation. Both cameras give the same results for a PSF full width half maximum larger than 1.5 pixels. All these simulations are applied to the A STEP (Antarctica Search for Transiting Extrasolar Planets) project. As a result, we choose a front‐illuminated camera for A STEP because of its better resolution and lower price, and we will use a PSF larger than 1.6 pixels. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The sun‐as‐a‐star solar spectrum

The Sun is the only star for which individual surface features can be observed directly. For other stars, the properties of starspots, stellar rotation, stellar flares, etc, are derived indirectly via variation of star‐integrated spectral line profiles or their luminosity measurements. Solar disk‐integrated and disk‐resolved observations allow for investigations of the contribution of individual solar disk features to sun‐as‐a‐star spectra. Here, we provide a brief overview of three sun‐as‐a‐star programs, currently in operation, and describe recent improvements in observations and data reduction for the Integrated Sunlight Spectrometer (ISS), one of three instruments comprising the Synoptic Optical Long‐term Investigations of the Sun (SOLIS) system. Next, we discuss studies employing sun‐as‐a‐star observations (including Ca II K line as proxy for total unsigned magnetic flux and 2800 MHz radio flux) as well as the effects of flares on solar disk‐integrated spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Field optimization and CCD data simulation for the antarctic International Concordia Explorer Telescope (ICE‐T)

We performed extensive data simulations for the planned ultra‐wide‐field, high‐precision photometric telescope ICE‐T (International Concordia Explorer Telescope). ICE‐T consists of two 60 cm‐aperture Schmidt telescopes with a joint field of view simultaneously in two photometric bandpasses. Two CCD cameras, each with a single 10.3k × 10.3k thinned back‐illuminated device, would image a sky field of 65 square degrees. Given a location of the telescope at Dome C on the East Antarctic Plateau, we searched for the star fields that best exploit the technical capabilities of the instrument and the site. We considered the effects of diurnal air mass and refraction variations, solar and lunar interference, interstellar absorption, overexposing of bright stars and ghosts, crowding by background stars, and the ratio of dwarf to giant stars in the field. Using NOMAD, SSA, Tycho‐2 and 2MASS‐based stellar positions and BVIJH magnitudes for these fields, we simulated the effects of the telescope's point‐spread‐function, the integration, and the co‐addition times. Simulations of transit light curves are presented for the selected star fields and convolved with the expected instrumental characteristics. For the brightest stars, we showed that ICE‐T should be capable of detecting a 2 R_Earth Super Earth around a G2 solar‐type star, as well as an Earth around an M0‐star – if these targets were as abundant as hot Jupiters. Simultaneously, the telescope would monitor the host star's surface activity in an astrophysically interpretable manner (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

FIES: The high‐resolution Fiber‐fed Echelle Spectrograph at the Nordic Optical Telescope

FIES is a cross‐dispersed high‐resolution echelle spectrograph at the 2.56 m Nordic Optical Telescope (NOT), and was optimised for throughput and stability in 2006. The major 2006 upgrade involved the relocation of FIES to a stable environment and development of a fiber bundle that offers 3 different resolution modes, and made FIES an attractive tool for the user community of the NOT. Radial‐velocity stability is achieved through double‐chamber active temperature control. A dedicated data reduction tool, FIEStool, was developed. As a result of these upgrades, FIES is now one of the work‐horse instruments at the NOT. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐ray energy spectra of CAL87

We present X‐ray spectral analysis of the super‐soft source CAL87 using ASCA, Chandra, XMM‐Newton observations. Early ASCA CCD spectrum reported a strong oxygen absorption edge, which is considered to originate in the an optically thick white‐dwarf atmosphere. On the other hand, contemporaneous grating observations by Chandra and XMM‐Newton indicate emission line dominated spectra, which obviously indicate the optically thin origin. Fitting all the available CCD (ASCA and XMM‐Newton) and grating spectra (XMM‐Newton and Chandra) simultaneously, we show that the CAL87 X‐ray energy spectrum is in fact composed of both an optically thick component with deep absorption edges and an optically thin component with numerous emission lines. The current result supports the standard SSS model that the primary source of X‐ray emission is nuclear burning in the white dwarf atmosphere, surrounded by a highly photoionised, optically thin corona (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facilities at ARIES for the Nainital-Cape Survey

A collaborative programme searching for mmag pulsations in chemically peculiar stars in the northern hemisphere was initiated in 1997 between Nainital, India, and Cape Town, South Africa. It was therefore named as theNainital-Cape Survey programme. The detection limits imposed by the observing conditions (including atmospheric noise and telescope size) at both Manora Peak and Devasthal sites are described. The scintillation noise on the best photometric nights is≈ 0.1 to 0.2 mmag for these sites. Both places allow one to detect few mmag variation in bright stars(B ≤ 12 mag), and are therefore particularly well-suited for carrying out the proposed survey work. The main characteristics of the three-channel photometer developed at ARIES for carrying out the observations are also presented. This excellent instrument has been used extensively since 1999 at the f/13 Cassegrain focus of ARIES’ 104 cm telescope. In particular, it allowed the survey to result in the discovery of δ Scuti like pulsations in four Am stars, in one rapidly oscillating Ap star, and in a number of probable variables so far. The future prospects are then presented, which regard the acquisition of a high speed time series CCD photometer, a project to build a 3-metre class telescope at Devasthal, and collaborative observations with Indian and foreign astronomical sites.     

Star‐forming galaxies observed with X‐shooter

In the last couple of decades hundreds of studies have explored the nature of star‐forming galaxies at different redshifts. This contribution focuses on X‐shooter observations of star‐burst galaxies at 0 < z < 6 from commissioning runs, science verification, and regular observations, and demonstrates the capability of the new instrument in this competitive field. Observations of gravitationally lensed galaxies show that X‐shooter has no limitation in the redshift desert (1.4 < z < 2) where the strong optical emission lines are shifted to the near‐IR region. Physical properties of galaxies, such as masses, metallicities, abundance ratios, and star formation rates can be derived from observations with relatively short integration times for faint galaxies. The simultaneous UV to near‐IR spectral coverage makes derivation of physical quantities more reliable because there are no differential slit losses as may occur when observations from different optical and near‐IR instruments are used. Over the entire redshift range, spectra of faint galaxies will allow us to better measure stellar ages and dominating ionisation sources compared to broad band spectral energy distribution measurements (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)