FLECHAS – A new échelle spectrograph at the University Observatory Jena

The new échelle spectrograph FLECHAS (Fibre Linked ECHelle Astronomical Spectrograph) is in operation at the Nasmyth‐focus of the 0.9 m telescope of the University Observatory Jena. FLECHAS is equipped with a sensitive back‐illuminated and midband coated CCD‐detector, as well as with a calibration unit for flatfield and wavelength‐calibration. The spectrograph covers the spectral range between about 3900 and 8100 Å and exhibits a resolving power of R ∼ 9300. In this article all technical characteristics of FLECHAS are described and examples of the first astronomical observations obtained with the new instrument in July 2013 at the University Observatory Jena are presented, among them the first light spectra taken with FLECHAS, simultaneous imaging and spectroscopic observations, the determination of the detection limit of the instrument, the spectroscopy of stars of different spectral types and of faint extended objects, as well as the Li‐line detection in the spectra of young solar‐like stars. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

p‐mode power variation with solar atmosphere as observed in the Na D1 and K spectral lines

In this work we investigate p‐mode power variation with solar atmosphere. To this aim, we use THÉMIS observations of the Na D1 (λ 5896 Å) and K (λ 7699 Å) spectral lines. While the formation heights of the K spectral line are essentially located in the photospheric layer, the formation heights of the Na D1 line span a much wider region: from photosphere up to chromosphere. Hence, we had the opportunity to infer p‐mode power variation up to the chromospheric layer. By analyzing power spectra obtained by temporal series at different points of the Na D1 and K spectral lines, we confirm and quantify the increase in p‐mode power towards higher atmospheric layers. Furthermore, the large span in formation heights of the Na D1 line induces a larger enhancement of p‐mode power with solar atmosphere compared to the K spectral line. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopy of solar prominences from space and ground

Two quiescent solar prominences were observed in July 2000 from SUMER aboard SOHO and from the two German solar telescopes at Tenerife. Two‐dimensional images taken at the VTT simultaneously in the spectral lines Hβ at 4862 Å and Ca II at 8542 Å show no significant spatial variation of their pressure‐sensitive emission ratio. Slit spectra of the Ca II 8542 Å and He I 10830 Å lines obtained at the Gregory‐Coudé telescope yield 8000 K < T_kin < 9000 K and 3 km/s < V_n–th < 8 km/s. Among the various spectral ranges observed with SUMER, we first investigate the Lyman emission lines, which were fitted by Gaussians yielding reliable spectral radiances and line widths for the series members 5 < k < 18. A determination of the level population gives for the lower series members a Boltzmann temperature of 60 000 K, the higher members being over‐populated. This temperature indicates an origin of the Lyman lines from hot surroundings of the cool prominence body seen in the ground‐based data; this also holds for the ‘hotter’ SUMER lines.     

Spectro‐polarimetry in the era of large solar telescopes

This paper discusses some of the challenges of spectro‐polarimetric observations with a large aperture solar telescope such as the ATST or the EST. The observer needs to reach a compromise between spatial and spectral resolution, time cadence, and signal‐to‐noise ratio, as only three of those four parameters can be pushed to the limit. Tunable filters and grating spectrographs provide a natural compromise as the former are more suitable for high‐spatial resolution observations while the latter are a better choice when one needs to work with many wavelengths at full spectral resolution. Given the requirements for the new science targeted by these facilities, it is important that 1) tunable filters have some multi‐wavelength capability; and 2) grating spectrographs have some 2D field of view (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

FIASCO: A new spectrograph at the University Observatory Jena

A new spectrograph (FIASCO) is in operation at the 0.9 m telescope of the University Observatory Jena. This article describes the characterization of the instrument and reports its first astronomical observations, among those lithium (6708 Å) detection in the atmosphere of young stars, and the simultaneous photometric and spectroscopic monitoring of variable stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic and velocity fields of active regions

We have observed about 15 active regions on the Sun, with the Advanced Stokes Polarimeter and Dick Dunn Telescope at NSO/SP to map the Stokes parameters in the photospheric Fe 6302.5 Å and chromospheric Mg I 5173 Å lines, during 1999‐2002. The observations are corrected for dark current, gain, instrumental polarization and cross‐talk using ASP pipeline. The wavelength calibration is carried out using the O₂ telluric line 6302 Å which is also present in the observations. The photospheric and chromospheric longitudinal magnetograms are made from the Stokes V profiles, which were intercalibrated with the Kitt Peak magnetograms. The plasma motions are inferred from the line bisector measurements at different positions of the spectral line. In this paper we present the height dependence of Doppler velocity scatter plots of a sunspot in the photospheric Fe I 6302 Å line.     

Imaging Spectropolarimeter for the Multi-Application Solar Telescope at Udaipur Solar Observatory: Characterization of Polarimeter and Preliminary Observations

The Multi-Application Solar Telescope (MAST) is a 50 cm off-axis Gregorian telescope that has recently become operational at the Udaipur Solar Observatory (USO). An imaging spectropolarimeter is being developed as one of the back-end instruments of MAST to gain a better understanding of the evolution and dynamics of solar magnetic and velocity fields. This system consists of a narrow-band filter and a polarimeter. The polarimeter includes a linear polarizer and two sets of liquid crystal variable retarders (LCVRs). The instrument is intended for simultaneous observations in the spectral lines 6173 Å and 8542 Å, which are formed in the photosphere and chromosphere, respectively. In this article, we present results from the characterization of the LCVRs for the spectral lines of interest and the response matrix of the polarimeter. We also present preliminary observations of an active region obtained using the spectropolarimeter. For verification purposes, we compare the Stokes observations of the active region obtained from the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with that of MAST observations in the spectral line 6173 Å. We find good agreement between the two observations, considering the fact that MAST observations are limited by seeing.     

Observations of Solar EUV Radiation with the CORONAS-F/SPIRIT and SOHO/EIT Instruments

The SPIRIT complex onboard the CORONAS-F satellite has routinely imaged the Sun in the 171, 175, 195, 284, and 304 Å spectral bands since August 2001. The complex incorporates two telescopes. The Ritchey-Chretien telescope operates in the 171, 195, 284, and 304 Å bands and has an objective similar to that of the SOHO/EIT instrument. The Herschel telescope obtains solar images synchronously in the 175 and 304 Å bands with two multilayer-coated parabolic mirrors. The SPIRIT program includes synoptic observations, studies of the dynamics of various structures on the solar disk and in the corona up to 5 solar radii, and coordinated observations with other spaceborne and ground-based telescopes. In particular, in the period 2002–2003, synoptic observations with the SPIRIT Ritchey-Chretien telescope were coordinated with regular 6-hour SOHO/EIT observations. Since June 2003, when EIT data were temporarily absent (SOHO keyholes), the SPIRIT telescope has performed synoptic observations at a wavelength of 175 A. These data were used by the Solar Influence Data Analysis Center (SIDC) at the Royal Observatory of Belgium for an early space weather forecast. We analyze the photometric and spectral parameters of the SPIRIT and EIT instruments and compare the integrated (over the solar disk) EUV fluxes using solar images obtained with these instruments during the CORONAS-F flight from August 2001 through December 2003.     

Time‐sensitive astronomy in non‐robotic telescopes

Protocols for dealing with time‐sensitive observations have traditionally focused on robotic telescope networks and other types of automated dedicated facilities, mostly in the optical domain. Using UKIRT and JCMT as examples, which are infrared and sub‐millimetre telescopes with a traditional PI‐dominated user base, we discuss how such facilities can join a heterogeneous telescope network to their mutual advantage. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Narrow-Band Imaging System for the Multi-application Solar Telescope at Udaipur Solar Observatory: Characterization of Lithium Niobate Etalons

The Multi-application Solar Telescope is a 50 cm off-axis Gregorian telescope that has been installed at the lake site of Udaipur Solar Observatory. For quasi-simultaneous photospheric and chromospheric observations, a narrow-band imager has been developed as one of the back-end instruments for this telescope. Narrow-band imaging is achieved using two lithium niobate Fabry–Perot etalons working in tandem as a filter. This filter can be tuned to different wavelengths by changing either voltage, tilt, or temperature of the etalons. To characterize the etalons, a Littrow spectrograph was set up in conjunction with a 15 cm Carl Zeiss Coudé solar telescope. The etalons were calibrated for the solar spectral lines Fe i 6173 Å, and Ca ii 8542 Å. In this work, we discuss the characterization of the Fabry–Perot etalons, specifically, the temperature and voltage tuning of the system for the spectral lines proposed for observations. We present the details of the calibration set-up and various tuning parameters. We also present solar images obtained using the system.     

A detailed view on the kinematics of candidate intermediate luminosity early‐type galaxies with a lack of dark matter

In several nearby L ∼ L_* early‐type galaxies, recent observations at large radii have shown indications of a lack of dark matter, substantially at odds with the prediction from the Cold Dark Matter (CDM) hierarchical merger models. Here we discuss a pilot observational project for the study of the internal kinematical and dynamical properties of this remarkable sample of galaxies. Using the VIMOS‐IFU in its high spectral resolution mode, it would be possible to investigate the regions up to ∼1.2 R_e, taking advantage of the much larger field of view and telescope diameter. This will allow to disclose the presence of any kinematical substructures which could affect the conclusion on the mass modeling and definitely clarify the inner structure of this particular class of early‐type galaxies. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

First Observations from the Multi-Application Solar Telescope (MAST) Narrow-Band Imager

The Multi-Application Solar Telescope is a 50 cm off-axis Gregorian telescope recently installed at the Udaipur Solar Observatory, India. In order to obtain near-simultaneous observations at photospheric and chromospheric heights, an imager optimized for two or more wavelengths is being integrated with the telescope. Two voltage-tuneable lithium-niobate Fabry–Perot etalons along with a set of interference blocking filters have been used for developing the imager. Both of the etalons are used in tandem for photospheric observations in Fe i 6173 Å and chromospheric observation in H\(\alpha\) 6563 Å spectral lines, whereas only one of the etalons is used for the chromospheric Ca II line at 8542 Å. The imager is also being used for spectropolarimetric observations. We discuss the characterization of the etalons at the above wavelengths, detail the integration of the imager with the telescope, and present a few sets of observations taken with the imager set-up.     

Spectroscopy of H II regions in the late-type spiral galaxy NGC 6946

We present the results of spectroscopy of 39 H II regions in the spiral galaxy NGC 6946. The spectral observations were carried out at the 6-m BTA telescope of the SAO RAS with the SCORPIO focal reducer in the multi-slit mode with the dispersion of 2.1 Å/px and spectral resolution of 10 Å. The absorption estimates for 39 H II regions were obtained. Using the “strong line” method (NS-calibration) we determined the electron temperature, and the abundances of oxygen and nitrogen for 30 H II regions. The radial gradients of O/H and N/H were constructed.     

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)     

Low‐frequency heliographic observations of the quiet Sun corona

We present new results of heliographic observations of quiet‐Sun radio emission fulfilled by the UTR‐2 radio telescope. The solar corona investigations have been made close to the last solar minimum (Cycle 23) in the late August and early September of 2010 by means of the two‐dimensional heliograph within 16.5–33 MHz. Moreover, the UTR‐2 radio telescope was used also as an 1‐D heliograph for one‐dimensional scanning of the Sun at the beginning of September 2010 as well as in short‐time observational campaigns in April and August of 2012. The average values of integral flux density of the undisturbed Sun continuum emission at different frequencies have been found. Using the data, we have determined the spectral index of quiet‐Sun radio emission in the range 16.5–200 MHz. It is equal to –2.1±0.1. The brightness distribution maps of outer solar corona at frequencies 20.0 MHz and 26.0 MHz have been obtained. The angular sizes of radio Sun were estimated. It is found that the solar corona at these frequencies is stretched‐out along equatorial direction. The coefficient of corona ellipticity varies slightly during above period. Its mean magnitudes are equal to ≈ 0.75 and ≈ 0.73 at 20.0 MHz and 26.0 MHz, respectively. The presented results for continuum emission of solar corona conform with being ones at higher frequencies. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Affordable échelle spectroscopy with a 60 cm telescope

A new fiber‐fed spectrograph was installed at the 60 cm telescope of the Stará Lesná Observatory. The article presents tests of its performance (spectral resolution, signal‐to‐noise ratio, radial‐velocity stability) and reports observations of selected variable stars and exoplanet host stars. First test observations show that the spectrograph is an ideal tool to observe bright eclipsing and spectroscopic binaries but also symbiotic and nova‐like stars. The radial‐velocity stability (60–80 m s^–1) is sufficient to study spectroscopic binaries and to detect easily the orbital motion of hot‐Jupiter extrasolar planets around bright stars. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

First Light of the Near-Infrared Narrow-Band Tunable Birefringent Filter at Big Bear Solar Observatory

We discuss a near-infrared (NIR) narrow-band tunable birefringent filter system newly developed by the Big Bear Solar Observatory (BBSO). This is one of the first narrow-bandpass NIR filter systems working at 1.56 μm which is used for the observation of the deepest solar photosphere. Four stages of calcite were used to obtain a bandpass of 2.5 Å along with a free spectral range (FSR) of 40 Å. Some unique techniques were implemented in the design, including liquid crystal variable retarders (LCVRs) to tune the bandpass in a range of ±100 Å, a wide field configuration to provide up to 2° incident angle, and oil-free structure to make it more compact and handy. After performing calibration and characteristic evaluation at the Evans Facility of the National Solar Observatory at Sacramento Peak (NSO/SP), a series of high-resolution filtergrams and imaging polarimetry observations were carried out with the Dunn Solar Telescope of NSO/SP and the 65-cm telescope of BBSO, in conjunction with the high-order adaptive optics system and the Fabry–Pérot Interferometer (FPI). In this paper, we describe the optical design and discuss the calibration method. Preliminary observations show that it is capable of serving as either a stand-alone narrow-band filter for NIR filtergram observations or an order-sorting filter of a FPI applied to NIR two-dimensional imaging spectro-polarimetry.     

Manifestations of Coronal Mass Ejections in the EUV Range from Data of the <Emphasis Type="Italic">CORONAS-F</Emphasis>/SPIRIT Telescope

We briefly overview results of our study of the large-scale solar activity associated with coronal mass ejections (CMEs). The observational material is constituted with data of the SPIRIT telescope aboard the CORONAS-F satellite in the three EUV channels 175, 284, and 304 Å. In particular, we consider a powerful geoeffective event of November 4, 2003, which was not observed by the SOHO/EIT telescope, a series of extremely powerful events of October 2003, and an event of November 18, 2003, with filament eruption. The efficiency of combined analysis of the SPIRIT and EIT data is demonstrated. The analysis confirms the coincidence of many dimmings in different spectral channels, including coronal lines with different excitation temperatures and the transition-region line, as well as the global character and homology of dimmings in recurrent events. The higher cadence SPIRIT observations at 304 Å reveal a slowly propagating large-scale darkening probably caused by absorption of emission in the dense, cold plasma of an eruptive filament.