Mechanical design of the solar telescope GREGOR

The mechanical structure of the GREGOR telescope was installed at the Observatorio del Teide, Tenerife, in 2004. New concepts for mounting and cooling of the 1.5‐meter primary mirror were introduced. GREGOR is an open telescope, therefore the dome is completely open during observations to allow for air flushing through the open, but stiff telescope structure. Backside cooling system of the primary mirror keeps the mirror surface close to ambient temperature to prevent mirror seeing. The large collecting area of the primary mirror results in high energy density at the field stop at the prime focus of the primary which needs to be removed. The optical elements are supported by precision alignment systems and should provide a stable solar image at the optical lab. The coudé train can be evacuated and serves as a natural barrier between the outer environmental conditions and the air‐conditioned optical laboratory with its sensitive scientific instrumentation. The telescope was successfully commissioned and will start its nominal operation during 2013 (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

HD 1: The number‐one star in the sky

We present the first ever study of the bright star HD 1. The star was chosen arbitrarily just because of its outstanding Henry Draper number. Surprisingly, almost nothing is known about this bright 7.^m4 star. Our observations were performed as part of the commissioning of the robotic telescope facility STELLA and its fiber‐fed high‐resolution optical echelle spectrograph SES in the years 2007–2010. We found long‐term radial velocity variations with a full amplitude of 9 km s^–1 with an average velocity of –29.8 km s^–1 and suggest the star to be a hitherto unknown single‐lined spectroscopic binary. A preliminary orbit with a period of 6.2 years (2279±69 days) and an eccentricity of 0.50±0.01 is given. Its rms uncertainty is just 73 m s^–1. HD 1 appears to be a G9‐K0 giant of luminosity class IIIa with T_eff = 4850±100 K, logg = 2.0±0.2, L ≈ 155 L_⊙, a mass of 3.0±0.3 M_⊙, a radius of 17.7 R_⊙, and an age of ≈350 Myr. A relative abundance analysis led to a metallicity of [Fe/H] = –0.12 ± 0.09. The α ‐element silicon may indicate an overabundance of +0.13 though. The low strengths of some s‐process lines and a lower limit for the ¹²C/¹³C isotope ratio of ≥16 indicate that HD 1 is on the first ascend of the RGB. The absorption spectral lines appear rotationally broadened with a v sin i of 5.5±1.2 km s^–1 but no chromospheric activity is evident. We also present photometric monitoring BV (RI)_C data taken in parallel with STELLA. The star is likely a small‐amplitude (<10 mmag) photometric variable although no periodicity was found (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spot activity on HD 89546 (FG UMa) from long‐term photometry

We present the analysis of 20 years of time‐series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B – V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9‐year time scale. We also find some evidence for brightness variability on a time scale longer than the 20‐year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.^m154, which is ≈0.^m2 brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B – V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip‐flop phenomenon. We estimate the differential rotation coefficient of the star as k = 0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45° (© 2011 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)     

Photometric investigations of distant comets C/2002 VQ94 (LINEAR) and 29P/Schwassmann-Wachmann-1

We present an analysis of the results of photometric investigations of two distant comets, C/2002 VQ94 (LINEAR) and 29P/Schwassmann-Wachmann-1, obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The comets under study demonstrate sufficient activity out of the zone of water ice sublimation (at heliocentric distances longer than 5 AU). In the spectra of the investigated comets, we found the CO⁺ and N₂⁺ emission. The presence of this emission may say that the comets were formed in the outer parts of the Solar System, in a protoplanetary cloud at a temperature ≤25 K. We found that the photometric maximum of the ionosphere (in the CO⁺ filter) of the comet C/2002 VQ94 (LINEAR) is shifted relative to the photometric center of the dust coma by 1.4″ (7.44 × 10³ km) in the direction deflected by 63° from the direction to the Sun. Using special filters to process the images, we picked out active structures (jets) in the dust coma of the 29P/Schwassmann-Wachmann-1 comet.     

The Torun catalogue of 6.7 GHz methanol masers

We report the observations of 289 methanol maser sources at 6.7 GHz obtained over a two month period with the Torun 32 m telescope. The data form a catalogue of all objects north of δ = –22° brighter than 7.5 Jy in the peak emission. The positions of sub‐arcsecond accuracy are updated for 76 % of the objects. We find that about one third of the sources show changes in the peak fluxes by a factor of two or more on time scales of 8.5–9.5 years (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hα line measurements from ten diffuse galactic sources using the DEFPOS facility

The hydrogen Balmer‐α emission line spectrum of ten diffuse ionization sources in the Milk Way – NGC 40 (WC8), NGC 2022, NGC 6210, NGC 6618 (M17, Sh2‐45), NGC 6720 (M57), NGC 6781, NGC 6888 (Sh2‐105), NGC 6992 (Sh2‐103), NGC 7635 (Sh2‐162,) and IC 1848 (Sh2‐199) – has been investigated using a dual etalon Fabry‐Pérot optical spectrometer (DEFPOS) aatached to the 150 cm RTT150 telescope at TUBITAK National Observatory (TUG, Antalya, Turkey: 36° 51′ N; 30° 20′ E; elevation: 2547 m). All of our galactic Hα observations discussed in this paper were carried out during the nights of 2013 June 21–24 with exposure time of 3600 s. As main results the intensity, the full width at half maximum, and the radial velocity with respect to the LSR have been determined for each data set. The intensities, the radial velocities, and the line widths of the Hα emission line vary from 59.15 to 8923.44 R, –46.72 to +54.07 km s^–1, and 31.4 to 48.01 km s^–1, respectively. The radial velocities and the half‐widths of the Hii regions and planetary nebulae determined from our measurements are found tobe consistent with values given in literature, especially with those in Schneider et al. (1983) and Fich et al. (1990). (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

NLST: India's National Large Solar Telescope

This article introduces the new Indian 2 m telescope which has been designed by MT Mechatronics in a detailed conceptual design study for the Indian Institute of Astrophysics, Bangalore. We describe the background of the project and the science goals which shall be addressed with this telescope. NLST is a solar telescope with high optical throughput and will be equipped with an integrated Adaptive Optics system. It is optimized for a site with the kind of seeing and wind conditions as they are expected at a lake site in the Himalayan mountains. The telescope can also be used for certain night time applications. We also give the scientific rationale for this class of telescope (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High‐order adaptive optical system for Big Bear Solar Observatory

A high‐order Adaptive Optical (AO) system for the 65 cm vacuum telescope of the Big Bear Solar Observatory (BBSO) is presented. The Coudé‐exit of the telescope has been modified to accommodate the AO system and two imaging magnetograph systems for visible‐light and near infrared (NIR) observations. A small elliptical tip/tilt mirror directs the light into an optical laboratory on the observatory's 2^nd floor just below the observing floor. A deformable mirror (DM) with 77 mm diameter is located on an optical table where it serves two wave‐front sensors (WFS), a correlation tracker (CT) and Shack‐Hartman (SH) sensor for the high‐order AO system, and the scientific channels with the imaging magnetographs. The two‐axis tip/tilt platform has a resonance frequency around 3.3 kHz and tilt range of about 2 mrad, which corresponds to about 25″ in the sky. Based on 32 × 32 pixel images, the CT detects image displacements between a reference frame and real‐time frames at a rate of 2 kHz. High‐order wave‐front aberrations are detected in the SH WFS channel from slope measurements derived from 76 sub‐apertures, which are recorded with 1,280 × 1,024 pixel Complex Metal Oxide Semiconductor (CMOS) camera manufactured by Photobit camera. In the 4 × 4 pixel binning mode, the data acquisition rate of the CMOS device is more than 2 kHz. Both visible‐light and NIR imaging magnetographs use Fabry‐Pérot etalons in telecentric configurations for two‐dimensional spectro‐polarimetry. The optical design of the AO system allows using small aperture prefilters, such as interference or Lyot filters, and 70 mm diameter Fabry‐Pérot etalons covering a field‐of‐view (FOV) of about 180″ × 180″.     

Photometric monitoring of the young star Par 1724 in Orion

We report new photometric observations of the ∼200 000 year old naked weak‐line run‐away T Tauri star Par 1724, located north of the Trapezium cluster in Orion. We observed in the broad band filters B, V, R, and I using the 90 cm Dutch telescope on La Silla, the 80 cm Wendelstein telescope, and a 25 cm telescope of the University Observatory Jena in Großschwabhausen near Jena. The photometric data in V and R are consistent with a ∼5.7 day rotation period due to spots, as observed before between 1960ies and 2000. Also, for the first time, we present evidence for a long‐term 9 or 17.5 year cycle in photometric data (V band) of such a young star, a cycle similar to that to of the Sun and other active stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The NST: First results and some lessons for ATST and EST

In January 2009, first light observations with the NST (New Solar Telescope) in Big Bear Solar Observatory (BBSO) were made. NST has a 1.7 m primary with a 1.6 m clear aperture. First observational results in TiO and Hα are shown and discussed. The NST primary mirror is the most aspheric telescope mirror deployed to date. The NST is early in its commissioning, and the plans for this phase will be sketched. Lessons learned in building and implementing the NST are germane for the ATST and EST telescopes and will be discussed. The NST has an off‐axis Gregorian configuration consisting of a parabolic primary, heat‐stop, elliptical secondary and diagonal flats. The focal ratio of the primary mirror is f/2.4. The working wavelength range covers from 0.4 to 1.7 µm in the Coudé Lab beneath the telescope and all wavelengths including the far infrared at the Nasmyth focus on the dome floor (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The power of low‐resolution spectroscopy: On the spectral classification of planet candidates in the ground‐based CoRoT follow‐up

Planetary transits detected by the CoRoT mission can be mimicked by a low‐mass star in orbit around a giant star. Spectral classification helps to identify the giant stars and also early‐type stars which are often excluded from further follow‐up. We study the potential and the limitations of low‐resolution spectroscopy to improve the photometric spectral types of CoRoT candidates. In particular, we want to study the influence of the signal‐to‐noise ratio (SNR) of the target spectrum in a quantitative way. We built an own template library and investigate whether a template library from the literature is able to reproduce the classifications. Including previous photometric estimates, we show how the additional spectroscopic information improves the constraints on spectral type. Low‐resolution spectroscopy (R ≈ 1000) of 42 CoRoT targets covering a wide range in SNR (1–437) and of 149 templates was obtained in 2012–2013 with the Nasmyth spectrograph at the Tautenburg 2 m telescope. Spectral types have been derived automatically by comparing with the observed template spectra. The classification has been repeated with the external CFLIB library. The spectral class obtained with the external library agrees within a few sub‐classes when the target spectrum has a SNR of about 100 at least. While the photometric spectral type can deviate by an entire spectral class, the photometric luminosity classification is as close as a spectroscopic classification with the external library. A low SNR of the target spectrum limits the attainable accuracy of classification more strongly than the use of external templates or photometry. Furthermore we found that low‐resolution reconnaissance spectroscopy ensures that good planet candidates are kept that would otherwise be discarded based on photometric spectral type alone. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

用于测量圆顶视宁度的微温脉动仪的研制

为评价云南天文台丽江2.4m望远镜的圆顶视宁度,研制了一种能测量温度、气压和微温脉动的仪器。在天文圆顶附近,望远镜前方光路上,放置几组微温传感器,可以测得圆顶附近影响天文观测的湍流强度的分布情况。介绍了这套仪器的基本原理,电路设计,程序设计,实验定标以及一个简单的测试。     

An experimental study on kinetically‐driven precipitation of calcium‐magnesium‐iron carbonates from solution: Implications for the low‐temperature formation of carbonates in martian meteorite Allan Hills 84001

Abstract— Spherical carbonate globules of similar composition, size, and radial Ca‐, Mg‐, and Fe‐zonation to those in martian meteorite Allan Hills (ALH) 84001 were precipitated from Mg‐rich, supersaturated solutions of Ca‐Mg‐Fe‐CO₂‐H₂O at 150 °C. The supersaturated solutions (pH ? 6–7) were prepared at room temperature and contained in Teflon^TM‐lined stainless steel vessels, which were sealed and heated to 150 °C for 24 h. Experiments were also conducted at 25 °C and no globules comparable to those of ALH 84001 were precipitated. Instead, amorphous Fe‐rich carbonates were formed after 24 h and Mg‐Fe calcites formed after 96 h. These experiments suggest a possible low‐temperature inorganic origin for the carbonates in martian meteorite ALH 84001.     

Observations of Near-Earth Asteroids in Polarized Light

We report the results of position, photometric, and polarimetric observations of two near-Earth asteroids made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. 1.2-hour measurements of the photometric variations of the asteroid 2009 DL46 made onMarch 8, 2016 (approximately 20^m at a distance of about 0.23 AU from the Earth) showed a 0.^m2-amplitude flash with a duration of about 20 minutes. During this time the polarization degree increased from the average level of 2–3% to 14%. The angle of the polarization plane and the phase angle were equal to 113° ± 1° and 43°, respectively. Our result indicates that the surface of the rotating asteroid (the rotation period of about 2.5 hours) must be non-uniformly rough. Observations of another asteroid—1994 UG—whose brightness was of about 17^m and which was located at a geocentric distance of 0.077 AU, were carried out during the night of March 6/7, 2016 in two modes: photometric and spectropolarimetric. According to the results of photometric observations in Johnson’s B-, V-, and R-band filters, over one hour the brightness of the asteroid remained unchanged within the measurement errors (about 0.^m02). Spectropolarimetric observations in the 420–800 nm wavelength interval showed the polarization degree to decrease from 8% in the blue part of the spectrum to 2% in the red part with the phase angle equal to 44?, which is typical for S-type near-Earth asteroids.     

The GREGOR adaptive optics system

The new 1.5‐m German solar telescope GREGOR at the Observatorio del Teide, Tenerife, is equipped with an integrated adaptive optics system. Although partly still in the commissioning phase, the system is already being used used for most science observations. It is designed to provide diffraction‐limited observations in the visible‐light regime for seeing better than 1.2″. We describe the AO system including the optical design, software, wavefront reconstruction, and performance (© 2012 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)     

膜圆顶及塔架对南极望远镜风载影响的仿真分析

为了充分利用Dome A地区绝佳的视宁度条件, 计划将南极望远镜安装在15m高的塔架上并使用轻质膜圆顶. 研究了在塔架和膜圆顶作用下风载对望远镜观测环境的影 响, 利用计算流体力学(Computational Fluid Dynamics, CFD)分析了在10m·s^-1稳态风作用下,不同风向角、方位轴转动角以及镜筒转动角时,望远镜周围风速、湍动能的分布情况以及光程差的变化,同时研究了风屏对风速、湍动能的改善作用和带来的温升.结果表明,塔架和圆顶周围的风速与湍动能分布对风向的改变不敏感;迎风状态时望远镜附近的湍流分布与风速分布情况整体优于背风状态;当风速为10m·s^-1时,在距离风屏1m远、3m高的位置处风速降为来流风速的1/3至1/4,望远镜附近的平均温升值为0.044 K.     

Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.     

Pendular seismometer for correcting telescope vibrations

Vibrations of telescopes can be successfully corrected in real time using a seismometer as an inertial reference. A prototype pendular seismometer is described that is suitable for angular vibration measurements at frequencies from a few tenths to several tens of Hz. The average pendulum position is maintained by a slow servo system that also damps its resonance. The prototype instrument has an rms noise of 3 milliarcsec in the 0–25-Hz band. It was tested on a 1-m telescope, and a good agreement of the seismometer signal with the direct optical measurements of the optical axis fluctuations of the telescope was found. A frequency response of the seismometer is studied, an expression for the rms amplitude of residual (uncompensated) vibrations is given. In space applications it is suggested that a pendular mirror in front of the telescope is used as an inertial reference for vibration correction.