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1.
HERMES, a fibre‐fed high‐resolution (R = 85000) échelle spectrograph with good stability and excellent throughput, is the work‐horse instrument of the 1.2‐m Mercator telescope on La Palma. HERMES targets building up time series of high‐quality data of variable stellar phenomena, mainly for asteroseismology and binary‐evolution research. In this paper we present the HERMES project and discuss the instrument design, performance, and a future upgrade. We also present some results of the first four years of HERMES observations. We illustrate the value of small telescopes, equipped with efficient instrumentation, for high‐resolution spectroscopy. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
The dependence on the temperature of photospheric line‐depth ratios (LDRs) in the spectral range 6190–6280 Å is investigated by using a sample of 174 ELODIE Archive stellar spectra of luminosity class from V to III. The rotational broadening effect on LDRs is also studied. We provide useful calibrations of effective temperature versus LDRs for giant and main sequence stars with 3800 ≃ Teff ≃6000 K and v sin i in the range 0–30 km s–1. We found that, with the exception of very few line pairs, LDRs, measured at a spectral resolution as high as 42 000, depend on v sin i and that, by neglecting the rotational broadening effect, the Teff determination can be wrong by ∼100 K in the worst cases. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
F. Kneer  F. Stolpe 《Solar physics》1996,164(1-2):303-310
This contribution deals with the properties of small-scale magnetic elements in plages. Spectro-polarimetric observations, obtained with the highest possible spatial resolution with the German solar telescopes at the Observatorio del Teide on Tenerife, were analysed. We conclude from the spread of line parameters measured in the Stokes I and V profiles of Fe I and Fe II lines that a wide range of magnetic properties is realised in the solar atmosphere. The flow velocities in small-scale magnetic flux tubes, deduced from the zero-crossing of the V profiles at high spatial resolution, show a fluctuation of v Doppler = 580 m s-1. This is substantially smaller than the turbulent broadening velocities of v Doppler = 2 – 3 km s–1 commonly derived by fitting V profiles from flux tube models to low spatial resolution data, e.g. from a Fourier Transform Spectrometer. Attempts to explain the high resolution I and V profiles by models of hydrostatic flux tubes are discussed. It appears impossible to accomplish agreement between the modeled and observed radiation of lines with strong and weak magnetic sensitivity at the same time. We suggest a scenario in which small-scale magnetic elements possess substructure and are dynamic, with gas flows and magnetic field strengths varying in space and time.  相似文献   

4.
Measuring distances to galaxies, determining their chemical composition, investigating the nature of their stellar populations and the absorbing properties of their interstellar medium are fundamental activities in modern extragalactic astronomy helping to understand the evolution of galaxies and the expanding universe. The optically brightest stars in the universe, blue supergiants of spectral A and B, are unique tools for these purposes. With absolute visual magnitudes up to MV ≃ ‐9.5 they are ideal to obtain accurate quantitative information about galaxies through the powerful modern methods of quantitative stellar spectroscopy. The spectral analysis of individual blue supergiant targets provides invaluable information about chemical abundances and abundance gradients, which is more comprehensive than the one obtained from HII regions, as it includes additional atomic species, and which is also more accurate, since it avoids the systematic uncertainties inherent in the strong line studies usually applied to the HII regions of spiral galaxies beyond the Local Group. Simultaneously, the spectral analysis yields stellar parameters and interstellar extinction for each individual supergiant target, which provides an alternative very accurate way to determine extragalactic distances through a newly developed method, called the Flux‐weighted Gravity–Luminosity Relationship (FGLR). With the present generation of 10 m‐class telescopes these spectroscopic studies can reach out to distances of 10 Mpc. The new generation of 30 m‐class telescopes will allow to extend this work out to 30 Mpc, a substantial volume of the local universe (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
We describe the properties of Mini-MegaTORTORA (MMT-9) nine-channel wide-field optical sky monitoring system with subsecond temporal resolution. This instrument can observe sky areas as large as 900 deg2, perform photometry in three filters close to Johnson BV R system and polarimetry of selected objects or areas with 100–300 deg2 sizes. The limiting magnitude of the system is up to V = 11m for 0.1 s temporal resolution, and reaches V = 15m in minute-long exposures. The system is equipped with a powerful computing facility and dedicated software pipeline allowing it to perform automatic detection, real-time classification, and investigation of transient events of different nature located both in the near- Earth space and at extragalactic distances. The objects routinely detected by MMT-9 include faint meteors and artificial Earth satellites.We discuss astronomical tasks that can be solved using MMT-9, and present the results of the first two years of its operation. In particular, we report the parameters of the optical flare detected on June 25, 2016, which accompanied the gamma-ray burst GRB160625B.  相似文献   

6.
In this paper we present Physical Parameter Eclipse Mapping (PPEM) of UBVRI eclipse light curves of UU Aqr from high to low states. We used a simple, pure hydrogen LTE model to derive the temperature and surface density distribution in the accretion disc. The reconstructed effective temperatures in the disc range between 9000 K and 15000 K in the inner part of the disc and below 7000 K in the outer parts. In the higher states it shows a more or less prominent bright spot with Teff between about 7000 K and 8000 K. The inner part of the disc (R < 0.3R) isL1 optically thick at all times, while the outer parts of the disc up to the disc edge (0.51 ± 0.04RL1 in the high state and 0.40 ± 0.03RL1 in the low state) deviate from a simple black body spectrum indicating that either the outer disc is optically thin or it shows a temperature inversion in the vertical direction. While during high state the disc is variable, it appears rather stable in low state. The variation during high state affects the size of the optically thick part of the disc, the white dwarf or boundary layer temperature and the uneclipsed component (originating in a disc chromosphere and/or cool disc wind), while the actual size of the disc remains constant. The difference between high and low state is expressed as a change in disc size that also affects the size of the optically thick part of the disc and the presence of the bright spot. Using the PPEM method we retrieve a distance for UU Aqr of 207±10 pc, compatible with previous estimates.  相似文献   

7.
To achieve high spatial resolution capability for IR solar observations, we suggest the use of a special mask placed before the entrance aperture of large conventional optical telescopes. Such a mask would match well the resolution of a non-redundant array and would provide safe operation of a large telescope used for solar observations. The proposed solution has the additional advantage of relatively low cost because already-existing optical telescopes are used.  相似文献   

8.
SARG is a cross dispersed echelle spectrograph in operation since late spring 2000 at the Italian Telescopio Nazionale Galileo (TNG) 3.5 m telescope, La Palma. SARG offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from λ = 0.37 up to1 μm, with resolution ranging from R = 29,000 up to R = 164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048 × 4096 EEV CCDs (pixel size: 13.5 μm) allowing complete spectral coverage at all resolving power for λ < 0.8 μm. In order to reach a high wavelength calibration precision an iodine-absorbing cell is provided. A Distributed Active Temperature Control System (DATCS) maintains constant the temperature of all spectrograph components at a preset value. Early results show that SARG works according to original specifications in terms of wavelength coverage, efficiency (measured peak efficiency is about 13%),resolution (maximum resolution R = 164,000 using a 0.3 arcsec slit, R ∼144,000 using an image slicer), and stability (preliminary estimates of radial velocity accuracy is ∼3 m/s using the iodine cell and ±150 m/s without the iodine cell). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
The inner disk rotation of NGC 6946 and the Milky Way is dominated by gravity but magnetism is not negligible at radii where the rotation curve becomes flat, and indeed could become dominant at very large radii. Values of the order of 1 μG, or even less, produce a centripetal force when the absolute value of the slope of the curve [B φ , R ] (azimuthal field strength versus radius) is less than the slope of a B φ ‐profile proportional to R –1. The ∝ R –1‐profile is here called the critical profile. From the hypothesis of magnetically driven rotation curves, the following is to be expected: at large radii, a “subcritical” profile (slope flatter than R –1); at still larger radii a B φ ‐profile becoming asymptotically critical as the density becomes asymptotically vanishing. Recent observations of magnetic fields in NGC 6946 and the Milky Way are in very good agreement with these predictions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
Morphological analyses of high resolution spectral recordings of Jovian decametric radiation show a regime of phenomena not seen at lower resolutions. Observed emissions range from narrowband (50 kHz) simple quasiperiodic bursts to wideband emissions (extending over a 500 kHz passband) exhibiting complex structural detail. Assuming gyroemission from electrons in a dipole field for which the magnetic moment is 10 Gauss RJ3, drift rate measurements of the bursts indicate that the source size is of the order of 600 km and its location is near R = 1.3 RJ at a colatitude of 27.3°. The measurements suggest that the emitting electrons belong to a population having a very specific equatorial pitch angle near 3.5°. This study concludes that it may be possible to verify gyroemission as the mechanism responsible for the decametric radiation.  相似文献   

11.
We present the results of our spectroscopic observations of the eclipsing binary SZ Cam performed with the 1-m (Zeiss-1000) and 6-m (BTA) telescopes at the Special Astrophysical Observatory of the Russian Academy of Sciences in 2000 and 2003. Based on our results and published data, we have calculated new values for the component mass ratio, q = 0.72 ± 0.02, the radial velocity of SZ Cam relative to the Solar system barycenter, V 0 =?10.6 ± 2.0 km s?1, and the semi-amplitudes of the radial velocity curves for both components, K 1 = 192.0 ± 2.6 and K 2 = 266.4 ± 2.5 km s?1. The orbital semimajor axes and masses of the components have been determined: α1 = 10.4R ⊙, α2 = 14.5R ⊙, M 1 = 16.7M ⊙, M 2 = 12.0M ⊙. New light elements and parameters of the radial velocity curve for the third body have been obtained. The mass of the secondary component of the third body M 2 3b is discussed. Its lower limit is estimated to be M 2 3b = 1.4M ⊙.  相似文献   

12.
PEPSI is the bench‐mounted, two‐arm, fibre‐fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2×8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Two 10.3k×10.3k CCDs with 9‐µm pixels and peak quantum efficiencies of 94–96 % record a total of 92 échelle orders. We introduce a new variant of a wave‐guide image slicer with 3, 5, and 7 slices and peak efficiencies between 92–96 %. A total of six cross dispersers cover the six wavelength settings of the spectrograph, two of them always simultaneously. These are made of a VPH‐grating sandwiched by two prisms. The peak efficiency of the system, including the telescope, is 15 % at 650 nm, and still 11 % and 10 % at 390 nm and 900 nm, respectively. In combination with the 110 m2 light‐collecting capability of the LBT, we expect a limiting magnitude of ≈20th mag in V in the low‐resolution mode. The R = 120 000 mode can also be used with two, dual‐beam Stokes IQUV polarimeters. The 270 000‐mode is made possible with the 7‐slice image slicer and a 100‐µm fibre through a projected sky aperture of 0.74″, comparable to the median seeing of the LBT site. The 43 000‐mode with 12‐pixel sampling per resolution element is our bad seeing or faint‐object mode. Any of the three resolution modes can either be used with sky fibers for simultaneous sky exposures or with light from a stabilized Fabry‐Pérot étalon for ultra‐precise radial velocities. CCD‐image processing is performed with the dedicated data‐reduction and analysis package PEPSI‐S4S. Its full error propagation through all image‐processing steps allows an adaptive selection of parameters by using statistical inferences and robust estimators. A solar feed makes use of PEPSI during day time and a 500‐m feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In this paper, we present the basic instrument design, its realization, and its characteristics. Some pre‐commissioning first‐light spectra shall demonstrate the basic functionality. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
Because of the limitations both from the slit width and the slit length of the spectrograph used in high resolution work, the efficiency of a telescope, with an aperture between D0 = 9m and D′0 = 55m, will be no better than that of a telescope with aperture D0. D0 can be identified as the maximum aperture of a ground-based telescope.  相似文献   

14.
A photometry in the V, R, I (Cousins) system has been performed for stars in the galaxy Cassiopeia 1. The resulting colour-agnitude (CM) diagram of Cas 1 reveals the existence of blue stars and the absence of red ones. From an analysis of the CM diagram of the galaxy it is concluded that Av = 4.0 mag, and the distance modulus (m – M)o = 24.5 mag, corresponding to a distance of 790 kpc. The visual magnitude of the galaxy is V = 14m.62 (Mv = −13m.8) and the colour index (V – R) = 0.89 mag. From the distance determination the galaxy Cassiopeia 1 is a member of the Local group.  相似文献   

15.
The Wolf-Rayet stars represent an advanced stage of evolution of the most massive stars. Their next immediate stadium will be supernova explosion. The most striking property of this very rare but exceptionally hot and bright objects is their extreme mass loss, of the order of 10-5 solar mass per year. In turn of evolution before and during the Wolf-Rayet phase such stars eject a lot of matter (∼ 10 M⊙) with velocity up to 3000 km/s that surrounds the min the form of gas and dust. In the case of binary Wolf-Rayet star such expanding envelope may interact with a companion (usually hot OB star) wind forming a tail extended for ∼ 100 AU. This spectacular phenomenon as well as some other connected with Wolf-Rayet stars that can be studied with high spatial resolution instruments (both astrometric and imaging) are reviewed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
This article discusses the interstellar extinction curve in the visible and the value of the ratio of absolute to selective extinction RV = AV/E (B – V). It is concluded that the visible extinction curve is likely to be linear in the visible and that indirect estimates of RV from tentative determinations of AV or from infrared and UV observations are questionable. There is currently no evidence of any variation of RV with direction. If RV is close to 3, as it has been inferred from mid‐infrared data, starlight in the visible is extinguished by a factor F /F0 = (2.5 e–2μm/λ)E (B –V). But if the visible wavelength range alone is considered, 4 appears as its most natural and probable value and F /F0 = e–2E (B –V)/λ (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
In this paper, we improve the previous work on the MHD Alfvén wave oscillation model for the neutron star (NS) kHz quasi‐periodic oscillations (QPOs), and compare the model with the updated twin kHz QPO data. For the 17 NS X‐ray sources with the simultaneously detected twin kHz QPO frequencies, the stellar mass M and radius R constraints are given by means of the derived parameter A in the model, which is associated with the averaged mass density of the star as 〈ρ 〉 = 3M /(4πR3) ≃ 2.4 × 1014 (A /0.7)2 g/cm3, and we also compare the M ‐R constraints with the stellar equations of state. Moreover, we also discuss the theoretical maximum kHz QPO frequency and maximum twin peak separation, and some expectations on SAX J1808.4–3658 are mentioned, such as its highest kHz QPO frequency ∼ 870 Hz, which is about 1.4–1.5 times less than those of the other known kHz QPO sources. The estimated magnetic fields for both Z sources (about Eddington accretion rate ) and Atoll sources (∼ 1% ) are approximately ∼109 G and ∼108 G, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
Faria  H. H.  Echer  E.  Rigozo  N. R.  Vieira  L. E. A.  Nordemann  D. J. R.  Prestes  A. 《Solar physics》2004,223(1-2):305-318
The objective of this paper is to compare the spectral features of the recently derived Group Sunspot Numbers (R G) and the traditional Wolf Sunspot Numbers (R Z) for the 1700–1995 period. In order to study the spectral features of both time series, two methods were used, including: (a) the multitaper analysis and (b) the wavelet analysis. Well-known features of the solar variability, such as the 98.6-yr (Gleissberg cycle), 10–11-yr (Schwabe cycle) and 5-yr (second solar harmonic) periodicities were identified with high confidence using the multitaper analysis. Also observed was a larger amount of power spread in high frequencies for R Z than for R G spectra. Furthermore, a multitaper analysis of two subsets, A (1700–1850) and B (1851–1995), has indicated that the main differences occurred in the first subset and seem to be due to uncertainties in the early observations. The wavelet transform, which allows observing the spectra evolution of both series, showed a strong and persistent 10–11-yr signal that remained during the whole period. The Meyer Wavelet Transform was applied to both R Z and R G. This study indicates that the main spectral characteristics of both series are similar and that their long-term variability has the same behavior.  相似文献   

19.
We have used two robotic telescopes to obtain time‐series high‐resolution optical echelle spectroscopy and VI and/or by photometry for a sample of 60 active stars, mostly binaries. Orbital solutions are presented for 26 double‐lined systems and for 19 single‐lined systems, seven of them for the first time but all of them with unprecedented phase coverage and accuracy. Eighteen systems turned out to be single stars. The total of 6609 R = 55000 échelle spectra are also used to systematically determine effective temperatures, gravities, metallicities, rotational velocities, lithium abundances and absolute Hα‐core fluxes as a function of time. The photometry is used to infer unspotted brightness, V – I and/or b – y colors, spot‐induced brightness amplitudes and precise rotation periods. An extra 22 radial‐velocity standard stars were monitored throughout the science observations and yield a new barycentric zero point for our STELLA/SES robotic system. Our data are complemented by literature data and are used to determine rotation‐temperature‐activity relations for active binary components. We also relate lithium abundance to rotation and surface temperature. We find that 74% of all known rapidly‐rotating active binary stars are synchronized and in circular orbits but 26% (61 systems) are rotating asynchronously of which half have Prot > Porb and e > 0. Because rotational synchronization is predicted to occur before orbital circularization active binaries should undergo an extra spin‐down besides tidal dissipation. We suspect this to be due to a magnetically channeled wind with its subsequent braking torque. We find a steep increase of rotation period with decreasing effective temperature for active stars, Prot α T–7eff, for both single and binaries, main sequence and evolved. For inactive, single giants with Prot > 100 d, the relation is much weaker, Prot α T‐1.12eff. Our data also indicate a period‐activity relation for Hα of the form RHα α P0.24rot for binaries and RHα α P‐0.14rot for singles. Its power‐law difference is possibly significant. Lithium abundances in our (field‐star) sample generally increase with effective temperature and are paralleled with an increase of the dispersion. The dispersion for binaries can be 1–2 orders of magnitude larger than for singles, peaking at an absolute spread of 3 orders of magnitude near Teff ≈ 5000 K. On average, binaries of comparable effective temperature appear to exhibit 0.25 dex less surface lithium than singles, as expected if the depletion mechanism is rotation dependent. We also find a trend of increased Li abundance with rotational period of form log n (Li) α –0.6 log Prot but again with a dispersion of as large as 3‐4 orders of magnitude (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
Absorption‐line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine‐structure constant, α, and the proton‐to‐electron mass ratio, μ = mp/me, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales which may reach a fractional level of ≈ 10 ppm (parts per million). We are conducting a Large Programme of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high‐resolution (R ≈ 60000) and high signal‐to‐noise ratio (S/N ≈ 100) spectra calibrated specifically to study the variations of the fundamental constants. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. (2013) and Rahmani et al. (2013). A stringent bound for Δα /α is obtained for the absorber at zabs = 1.6919 towards HE 2217‐2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in α in this system is +1.3 ± 2.4stat ± 1.0sys ppm if Al II λ 1670 Å and three FeII transitions are used, and +1.1 ± 2.6stat ppm in a slightly different analysis with only FeII transitions used. This is one of the tightest bounds on α ‐variation from an individual absorber and reveals no evidence for variation in α at the 3‐ppm precision level (1σ confidence). The expectation at this sky position of the recently‐reported dipolar variation of α is (3.2–5.4) ± 1.7 ppm depending on dipole model used and this constraint of Δα /α at face value is not supporting this expectation but not inconsistent with it at the 3σ level. For the proton‐to‐electron mass ratio the analysis of the H2 absorption lines of the zabs ≈ 2.4018 damped Lyα system towards HE 0027–1836 provides Δμ /μ = (–7.6 ± 8.1stat ± 6.3sys) ppm which is also consistent with a null variation. The cross‐correlation analysis between individual exposures taken over three years and comparison with almost simultaneous asteroid observations revealed the presence of a possible wavelength dependent velocity drift as well as of inter‐order distortions which probably dominate the systematic error and are a significant obstacle to achieve more accurate measurements. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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