CCD Exposures Research Articles

High-resolution spectra of solar magnetic features. I - Analysis of penumbral fine structure

view Abstract Citations (88) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Resolution Spectra of Solar Magnetic Features. I. Analysis of Penumbral Fine Structure Lites, B. W. ; Scharmer, G. B. ; Skumanich, A. Abstract The Swedish Vacuum Telescope on La Palma was used to obtain spectra of the magnetic-sensitive Fe I 630.25 nm line under conditions of exceptional angular resolution (0.32 arcsec) and high spectral resolution (FWHM 2.5 pm). Simultaneous 0.02 s CCD exposures of both the spectrum and the slit-jaw image effectively 'freeze' the atmospheric seeing motions and permit unambiguous identification of the spectra of the various penumbral structures. These spectra reveal the magnetic field strength in penumbral filaments through an intensity fit of the Zeeman splitting of this line. The observations show that: (1) the field strength varies from about 2100 G near the umbra-penumbra boundary to about 900 G at the outer edge of the penumbra, (2) the observed fluctuation of penumbral magnetic field is much less dramatic than the fluctuation in intensity, (3) there is a suggestion of a rapid change in field inclination between some light and dark filaments near the edge of the penumbra, and (4) there is no obvious correlation between Doppler shift (in part due to the Evershed flow) and filament intensity. Publication: The Astrophysical Journal Pub Date: May 1990 DOI: 10.1086/168767 Bibcode: 1990ApJ...355..329L Keywords: Fine Structure; Solar Magnetic Field; Solar Spectra; Sunspots; Iron; Penumbras; Solar Granulation; Solar Observatories; Solar Physics; SUN: MAGNETIC FIELDS; SUN: SUNSPOTS full text sources ADS | Related Materials (1) Part 2: 1991ApJ...373..683L

A Search for Companions to High Redshift (z ≥ 3.0) Quasars

Following the discovery by Djorgovski et al. (1985) of a companion to the high redshift quasar PKS 1614+051, we initiated a systematic search for such objects with the Danish 1.5 meter telescope at La Silla. The observing technique is CCD exposures in narrow filters (FWHM=100Å) centered on the redshifted Lyα. For an exposure time of 40 min. Our limiting magnitude is around 22.0 (where the r.m.s. error is approximately ±0.15), according to test runs with DAOPHOT. The aim of the search is to clarify the nature of such companions: are they “primordial” galaxies? Lyα clouds associated with the quasar? - and how frequent is such a phenomenon? Up to now we have covered 26 fields around quasars with redshift ≥3.0 (which is about 25% of all high redshift quasars in the Veron and Veron Catalogue). Furthermore 12 fields around z≈2.5 has also been observed (see Table 1). A quick visual inspection of all our frames has not revealed any companions except for the object found by Djorgovski et al. (which is easily picked up by our technique). However, a thorough photometric reduction (using DAOPHOT) might reveal fainter candidates. Taken together with the fields reported observed by Hu and Cowie (1987) and Djorgovski et al. (1987), a total of about 50 fields have so far been observed. The preliminary conclusion is therefore that such companions, whatever they might be, are very rare, and certainly much rarer than similar systems found around quasars of low redshift.

Photoelectric UBVRI sequences in the region of the galactic globular clusters NGC 362, NGC 1261, NGC 6656, and NGC 6809

view Abstract Citations (15) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoelectric UBVRI Sequences in the Region of the Galactic Globular Clusters NGC 362, NGC 1261, NGC 6656, and NGC 6809 Alcaino, Gonzalo ; Liller, William ; Alvarado, Franklin Abstract UBVRI photoelectric sequences for Galactic globular clusters NGC 362, NGC 1261, NGC 6656 (M22), and NGC 6809 (M55) are herewith presented. All of them include fields suitable for CCD exposures. Except for a few stars in NGC 362 and M22, no RI magnitudes have previously been published for these clusters. For NGC 362, 18 stars are in UBV in common with Harris (1982), and for NGC 6809, four stars are in UBV in common with Lee (1977). Publication: The Astronomical Journal Pub Date: July 1988 DOI: 10.1086/114796 Bibcode: 1988AJ.....96..139A Keywords: Astronomical Photometry; Globular Clusters; Ubv Spectra; Calibrating; Charge Coupled Devices; Color-Magnitude Diagram; Interstellar Extinction; Red Giant Stars; Astronomy; PHOTOMETRY; CLUSTERS: GLOBULAR full text sources ADS | data products SIMBAD (4) GCPD (1)

The shell system around NGC 3923 and its implications for the potential of the galaxy

A study of the shell galaxy NGC 3923 is presented. It is mainly based on CCD and photographic observations made at the CFHT, ESO, and AAT from 1982 to 1986. New shells have been discovered. The geometry of 22 shells is investigated in detail with an estimate of the uncertainties. The interleaving of the shells is not a clear as it has been claimed: it is well defined for the outer shells but the distances of the inner shells present a certain symmetry relative to the center. Shells have a roughly constant ellipticity of E = 1. +/- 0.4 [ E = 10 x ( 1 - b/a)]. It has been suggested by some authors that shell ellipticities are related to the elliptical potential; a brief study of current models of elliptical galaxies shows that the shell ellipticities are of the same magnitude as the equipotential ellipticities, but no clear relation id visible. Profiles were derived for 19 shells, and a simple model was fitted to these profiles. The shell thickness is typically of 0.17 kpc for the inner shells. The total B luminosity of the shell system is ~ 5 % (+/- 1 %) of the luminosity of the galaxy. The outermost shells are much more luminous than the inner ones: the outer four shells contribute ~85% of the total luminosity. A dust lane has been discovered on deep CCD exposures. If it is in a stable configuration its orientation is in contradiction with some previous studies based on numerical simulations which concluded that NGC 3923 was a prolate system. A photometric study of the galaxy is presented. The inferred central M/L ratio, is close to 10 which does not depart from the values usually found in ellipticals. Observations in the 21 cm hydrogen line with the Parkes Radio Telescope gives an upper limit of the H I content of 7 x 10^8 solar mass. The results of the present study seem compatible with the merging hypothesis but dynamical friction has to be invoked to account for the presence of the innermost shells we have observed.

Photographic Phtotometry of 4500 Stars in M 30

We present B and V photometry of ~ 4500 stars (V < 21.3 mag) within the region 2′.1 < r < 10′ centered on the southern globular cluster M 30 (NGC 7099), from two sets of four plates of the 4 m CTIO (CT) and the 2.5 m Dupont (LC) telescopes (Piotto 1986). Instrumental magnitudes (applying INVENTORY to PDS scans) are calibrated by four CCD exposures from the ESO 1.5 m Danish telescope. Our results removed the disagreement between previous photometry (Alcaino and Liller 1980) and the isochrones published by VandenBerg (1983).

Globular Clusters Detected in the Coma Cluster's Central Giant Galaxy NGC 4874

We have used the Canada-France-Hawaii Telescope on Mauna Kea to obtain two deep CCD exposures in the central region of the Coma cluster, and we have used the new images to detect globular clusters in the central giant galaxy NGC 4874. One exposure with a total integration time of 2 hours lies in the halo of the giant galaxy. A second (comparison) exposure of the same integration time was taken within the cluster core but well away from any other bright galaxy. Our analysis, which includes both photometry and image classification with the automated routines called FOCAS, extends to a limiting B magnitude of 26.25. Image classification is a necessary part of this study because at the faintest limiting magnitudes globular clusters are easily confused with the rich population of faint background galaxies. We have been particularly successful in sorting stellar objects from galaxies because the image quality on our images is quite good: FWHM ~ 0.6 arcsec. The data were taken with the fast autoguiding instrument called ISIS (Thompson and Ryerson 1984)

The nonradial oscillations of Epsilon Persei. II - Nonlinear characteristics

During five nights in 1984 November the authors obtained over 300 high quality CCD exposures of the Si III λ4552-4574 lines in ɛ Persei (B0.7 III), a star with remarkably large line profile variations. Detailed line profile models have been computed for a sample of over 60 of them, and these show that the variations are described well in the framework of nonradial pulsation (NRP) by two modes, a dominant one described by -m = l = 4 (mean period, 3.85±0.02 hr) and a secondary one by -m = l = 6 (2.25±0.3 hr). This study provides also a definition of the nonlinear properties of NRP waves, which can show extreme variations in amplitude both in time and around the wave pattern. The analysis suggests a simple picture in which a wave becomes marginally supersonic in the stellar atmosphere, develops an increasingly nonsinusoidal waveform, and partially loses its coherence by interfering with itself as it circuits the star.

BVRI photometry of extragalactic cepheids and new insights for the distance scale

We present new BVRI photoelectric photometry of long-period Cepheids in the Large and Small Magellanic Clouds. Period-luminosity relations based on both time-averaged and single, random-phased data are discussed, and it is shown that at wavelengths longward of the R bandpass the randomly phased data should give a spread at fixed period which is always less than the time-averaged B period-luminosity relation. Single-epoch data for five Cepheids measured in CCD exposures of a single field in M33 are used to illustrate the power of the random-phase period-luminosity relation for the Cepheid distance scale.

X-ray and optical variability at the hour timescale for 1E 0630+178 (GEMINGA) and its proposed optical couterpart

Einstein and EXOSAT data on the soft X-ray source IE 0630+178, the proposed counterpart of the γ-ray source GEMINGA, are analyzed for variability on the time scale of one to three hours. The EXOSAT September 1983 data, with an uninterrupted strech of over 10 hours offer the most interesting case. In parallel, a similar analysis is presented for the first time, for the optical data of the mV∼21 proposed counterpart. About 30 CCD exposures, of 15 min. each, taken over two consecutive nights at the 3.6 m CFH telescope, yield evidence of variability, when compared to the data of similar nearby objects in the field.