Observatorio Del Roque De Los Research Articles

Time Series of Solar Granulation Images. II. Evolution of Individual Granules

The properties of the evolution of solar granulation have been studied using an 80 minute time series of high spatial resolution white-light images obtained with the Swedish Vacuum Solar Telescope at the Observatorio del Roque de los Muchachos, La Palma. An automatic tracking algorithm has been developed to follow the evolution of individual granules, and a sample of 2643 granules has been analyzed. To check the reliability of this automatic procedure, we have manually tracked a sample of 481 solar granules and compared the results of both procedures. An exponential law gives a good fit to the distribution of granular lifetimes, T. Our estimated mean lifetime is about 6 minutes, which is at the lower limit of the ample range of values reported in the literature. We note a linear increase in the time-averaged granular sizes and intensities with the lifetime. T=12 minutes marks a sizeable change in the slopes of these linear trends. Regarding the location of granules with respect to the meso- and supergranular flow field, we find only a small excess of long-lived granules in the upflows. Fragmentation, merging, and emergence from (or dissolution into) the background are the birth and death mechanisms detected, resulting in nine granular families from the combination of these six possibilities. A comparative study of these families leads to the following conclusions: (1) fragmentation is the most frequent birth mechanism, while merging is the most frequent death mechanism; (2) spontaneous emergence from the background occurs very rarely, but dissolution into the background is much more frequent; and (3) different granular mean lifetimes are determined for each of these families; the granules that are born and die by fragmentation have the longest mean lifetime (9.23 minutes). From a comparison of the evolution of granules belonging to the most populated families, two critical values appear for the initial area in a granular evolution: 0.8 Mm2 (dg=139) and 1.3 Mm2 (dg=177). These values mark limits characterizing the birth mechanism of a granule, and predict its evolution to some extent. The findings of the present work complement the earlier results presented in this series of papers and reinforce with new inputs, as far as the evolutionary aspects are concerned, the conclusion stated there that granules can be classified into two populations with different underlying physics. The boundary between these two classes could be established at the scale of dg=14.

Nitrogen Abundances in Damped Lyα Galaxies

Nitrogen lines of the N I λ1134 and λ1200 multiplets in the damped Lyα (DLA) galaxies at zabs = 2.309, 2.827, and 3.025 toward the QSOs 0100+1300, 1425+6039, and 0347-3819, respectively, have been detected by means of high-resolution spectra (R ~ 2 × 104) obtained with 4 m class telescopes at ESO (La Silla, Chile) and the Observatorio del Roque de los Muchachos (La Palma, Spain). The two N I multiplets offer a considerable range in oscillator strengths and the possibility of disentangling Lyα interlopers. The derived nitrogen abundances for the three damped systems are [N/H] = -2.68 ± 0.11, -1.57 ± 0.09, -2.07 ± 0.13, respectively. The behavior of nitrogen relative to iron-peak and α elements has been investigated by considering all the extant N I determinations for a total of nine DLA galaxies. We have estimated the fraction of iron locked into dust grains to convert the observed [N/Fe] ratios into overall (dust plus gas) relative abundances, [N/Fe]corr. The ratios [N/α] have been mostly determined by using sulphur as a tracer of α elements that is unaffected by dust. The [N/Fe] and [N/α] ratios show high dispersions, of 1 order of magnitude or more, which have no equivalent in other element-to-element ratios in DLAs. The lowest values of the [N/Fe]corr and [N/α] ratios are at variance with the values measured in Galactic halo stars of similar metallicity, suggesting that part of the DLA galaxies do not follow the chemical evolution of the Milky Way. The DLA nitrogen abundances and their dispersion show some similarities with those observed in dwarf galaxies. Comparison with chemical evolution models shows that the lowest [N/Fe]corr and [N/α] DLA values are close to what would be expected for a pure secondary origin of nitrogen, whereas higher values are mostly consistent with a primary component. The behavior of nitrogen abundance ratios can be ascribed, in general, to the delayed release of nitrogen in the course of evolution. However it is difficult to conciliate this interpretation with the lowest [N/α] values measured, since an expected enhancement of α elements with respect to the iron-peak elements is not observed simultaneously in these DLA galaxies. In two cases, relatively high [N/α] values are observed that require also a more complex chemical evolution to be explained.

An Optical Intermediate Dispersion Spectrograph for the GTC

ODIN is an international consortium constituted to design and build a first-light multi-purpose optical intermediate dispersion spectrograph for the Gran Telescopio Canarias (GTC, 10-m) to be installed at the Observatorio del Roque de los Muchachos (La Palma). This instrument should fulfill an important fraction of the needs of the Spanish astronomical community in optical spectroscopy performed at large telescopes, and must be highly competitive in a variety of research fields. We are proposing a spectrograph that will be capable of providing multi-object observations by means of optical fibers, integral field spectroscopy, and also multi-integral fields. It will be mounted at the Nasmyth focus of the GTC. One of the main drivers of our proposal is to cover the whole visible range allowed by the atmospheric cut-off with the highest efficiency, particularly at the UV end.

Night-time image quality at Roque de los Muchachos Observatory

Nine months' seeing statistics at the Observatorio del Roque de los Muchachos (ORM) are presented. Measurements were taken with a differential image motion monitor on top of a 5-m high tower. From the whole campaign the mean seeing is 0.76″, the median value is 0.64″ and 7% of the time the seeing is better than 0.3″. The best seeing measured is 0.17″. A seasonal variation is noticeable, better seeing conditions appearing during summer, which corresponds to the occurrence of a well-defined inversion layer due to the high prevalence of trade winds. During the summer, 50% of the time seeing is better than 0.54″, value which drops to 0.46″ during June, with a narrow distribution (rms = 0.17″). These figures place the ORM among, or better than, the best astronomical sites (Paranal and La Silla, Chile) where seeing statistics are available. When inspecting individual nights, it sporadically happens that seeing deteriorates abruptly and slowly recovers, with a 1.2-hour exponential decay time. This phenomenon is interpreted in terms of meteorological instabilities (gravity waves) which trigger a turbulent regime.

Time Series of Solar Granulation Images. I. Differences between Small and Large Granules in Quiet Regions

A 90 minute time series of high spatial resolution white-light images of solar granulation, obtained at the Swedish Vacuum Solar Tower (Observatorio del Roque de los Muchachos, La Palma), was analyzed to study how the physical properties of the granules changed with size. The observational material was corrected for global motions and for the instrumental profile, and a subsonic filter was applied. A definition of granular border was adopted using the inflection points of the intensity of the images, and the granular cells were defined as areas including, in addition to the granules, one-half of their surrounding intergranular lanes. Using time series to investigate the average behavior of solar granulation has three strong advantages: the first is the possibility of removing the acoustic waves; second, the possibility of estimating the effect of the variability of seeing on our results; and, third, the opportunity to attain high statistical significance in the analysis as a result of the large number of extracted granules (61,138). It is shown that the granules of the sample can be classified according to their mean and maximum intensities and their fractal dimension into two regimes, with diameters smaller than and larger than 14, respectively. A broad transition region in which both regimes coexist was found. The resolved internal brightness structure of both the granules and the intergranular lanes shows a linear increase of the number of substructures with the granular and intergranular areas. The diameters of these substructures range between our effective resolution limit (~03) and ~15, with preferential sizes at 065 and 055, respectively. Moreover, it seems that large and small granules are unevenly distributed with respect to the large-scale vertical flows. Thus smaller granules are more concentrated along downdrafts whereas larger ones preferentially occupy the updrafts. Finally, a physical scenario compatible with the existence of these two granular populations is discussed.

The Canaris Type IA Supernovae Archive (I)

This paper presents an atlas containing 59 low-resolution supernova <br>spectra which correspond to 27 type Ia supernovae. These 59 spectra spectra which correspond to 27 type Ia supernovae. These 59 spectra refer to different ages along the postmaximum type Ia evolution, covering from the photospheric to the old (~>300 days) nebular phases. These supernovae were observed as a part of the long-term observational program Supernova Monitoring Project, carried out at the Observatorio del Roque de los Muchachos (La Palma, Spain) from 1990 July to 1994 July. Most of these observations were taken with the Faint Object Spectrograph (FOS) and a few spectra were obtained by means the ISIS spectrograph. Three or more spectra were obtained for ten of these supernovae. Concerning the homogeneity among the type Ia supernova subclass, our sample points to a "first-order" overall homogeneous spectroscopic behavior. However, a finer analysis - comparing spectra at similar evolutionary phase-allows differences to be found in relation to strengths, wavelength positions, and evolution with time of the more significant spectral type Ia supernova features. Furthermore, some objects that exhibit clear signs of spectroscopic peculiarities (SNe 1991F, 1991bg, and 1991bj) are also included in our sample. The parent galaxies of these supernovae present redshifts ranging from z = 0.003 to z = 0.07. Four of these (SNe 1991S, 1991ad, 1992R, and 1992ac) were observed in galaxies with z~>0.05. Only six events in our sample were detected in an early-type (i.e., elliptical or lenticular) galaxy, whereas multiple supernova events were detected in five of the parent galaxies in our supernova sample.

Simultaneous Bidimensional Spectroscopy of Extened Objects Using Optical Fibers: Application to Seyfert Galaxies

AbstractIn this communication we summarize the main characteristics of three optical fiber systems, namely HEXAFLEX, HEXAFLEX-II, and 2D-FIS, developed for performing simultaneous bidimensional spectroscopy of extended objects. They have been used at the 4.2m William Herschel (WHT) and the 2.5m Nordic Optical Telescope (NOT), which are sited at the Observatorio del Roque de los Muchachos. These systems have been used to observe the circumnuclear regions of several Seyfert galaxies. They show clear advantages over other instruments based on more classical techniques, at least for these complex objects of small angular size on the sky. Some examples will be given to illustrate this.

A High-Resolution Study of Inhomogeneities in Sunspot Umbrae

view Abstract Citations (97) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A High-Resolution Study of Inhomogeneities in Sunspot Umbrae Sobotka, Michal ; Bonet, Jose A. ; Vazquez, Manuel Abstract A detailed study of the brightness, size, spatial distribution, and filling factor of the different umbral inhomogeneities is presented. Many sunspots show multiple umbrae (separated by strong light bridges, SLBs), which behave like independent units. These are termed umbral cores (UCs). From the phenomenological point of view, UCs show two components: (1) a dark area, formed by a diffuse background (DB), with local intensity minima called dark nuclei (DNs), and (2) bright features including umbral dots (UDs) and faint light bridges (FLBs). Slit-jaw images (bandpass 5425±50 Å) and spectra (line Fe I 5434.5 Å) of seven sunspots with 13 separate UCs were acquired using the Swedish Solar Telescope at the Observatorio del Roque de los Muchachos (La Palma) with a spatial resolution of 0".3. Image restoration and inversion of the spectral line profile were applied, with the following results: The most important photometric parameter of the UCs is the mean intensity of their DB (mean background intensity ‾Iback). It is well correlated to the intensity minimum of the diffuse background and to the mean brightness of UDs. The relation between the size of the UCs and their ‾Iback is not straightforward, but UCs with radii <5" are in general brighter than the larger ones. The differences in the brightness of individual umbrae can be explained mainly by variations of ‾Iback rather than in terms of variations of UD filling factor. The linear relation between the peak intensity of UDs and the intensity of the adjacent DB (local background intensity) was confirmed in a sample of more than 1500 elements, and the "true" peak-to-background ratio was estimated as 3. The spatial distribution of UDs is nonuniform. In DNs (whose size is comparable to that of photospheric granules) UDs appear very rarely; they prefer to form clusters and alignments outside the DNs. The mean nearest neighbor distance decreases, and the density of UDs increases with increasing ‾Iback. The filling factor of UDs is in the range 3%-10%, and the size of UDs is similar in all UCs. The typical "true" size is 180-300 km, and it is uncorrelated to the peak brightness of UDs. FLBs are composed of bright grains and dark spaces between them. The bright grains are darker than photospheric granules. The size of the bright grains is similar to that of UDs, and their relative area in FLBs is very close to the fractional area granulum-intergranulum in the quiet photosphere. On the basis of the obtained spectral profiles, working models of temperature stratification are presented for UDs, their adjacent DB, and DNs. On the basis of observational facts the following is proposed: UDs and FLBs are probably demonstrations of some kind of altered convection, with a cell size of about 0".5, modulated by a smoothly varying magnetic field. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173205 Bibcode: 1993ApJ...415..832S Keywords: SUN: SUNSPOTS full text sources ADS |

Shock Modelling of the Bipolar Outflow Source NGC 6537

NGC 6537 is an unusual high excitation bipolar outflow source, with anomalous abundances indicative of a type I nebula. We have recently obtained a range of high resolution spectrophotometry for this source using the 2.5 m Isaac Newton Telescope (Observatorio del Roque de Los Muchachos, La Palma), together with narrow band optical imaging using the 2.6 m Nordic Optical Telescope (Observatorio del Roque de los Muchachos, La Palma). As a consequence, it is apparent that the source optical morphology is suggestive of the presence of an hyperbolic shock outflow surface, similar to those observed in other BPN (e.g. NGC 6302, Hb 5). Line ratio maps also indicate the presence of extremely strong [Nii] emission at the periphery of the outflow, whilst expansion velocities are of order ∼ 400 km sec−1. These large shell expansion velocities may in turn be driven by an extremely high velocity wind, which in this case appears to extend over a range ΔV ≥ 3000 km sec−1.

Visual Extinction and Physical Conditions in the Bipolar Nebula M2-9

A detailed analysis of the visual extinction and physical conditions of the extreme bipolar nebula M2-9 has been made from optical spectra acquired with the Intermediate Dispersion Spectrograph of the 2.5m Isaac Newton Telescope (Observatorio del Roque de los Muchachos, La Palma) in combination with a 235mm camera and the IPCS detector covering the spectral range 3500-7500 Å with spectral resolution of 4 Å.

Analysis of Neckel and Chini standard stars in theUBVRI photometric system

This paper studies the list of 60 faint standard stars of Neckel and Chini (1980) in theUBVRI Johnson photometric system. These standards have been used due to the collaboration in the HIPPARCOS project of our department, but this work was made in parallel of this and the results were not used. We have re-reduced the standard stars using our own method of reduction from a large number of selected observations made at the Observatorio Astronomico Nacional and at the Centro Astronomico Hispano-Aleman, both at Calar Alto, Spain, and at the Observatorio del Roque de los Muchachos, La Palma Island, Spain. The reduction method used is explained and the results are given for the four colours used: (B-V),(U-B), (V-R), and (V-I), together with theV magnitude, that is, we have corrected many standard stars for each colour and magnitude. These results are supported with graphs where residual colour (o magnitude), is plotted against corresponding colour (or magnitude). Finally, our (V-R) and (V-I) results are compared to those of Tayloret al. (1989), with a good correspondence.

Double star CCD astrometry and photometry

About 3000 CCD measurements of double stars have been made in one or both filters V and R on the 1m Jacobus Kapteyn Telescope at La Palma. ∗ ∗ The Jacobus Kapteyn Telescope is operated on the island of La Palma by the Royal Greenwich Observatory in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The stars form part of the INput CAtalogue (INCA) of the astrometric satellite HIPPARCOS, and require both astrometry and photometry in order to facilitate reduction of the HIPPARCOS measurements. The primary components of the binaries have visual magnitudes between 8 m and 12 m, and the apparent separations between components range from 0″.5 to 30″. The difference in the separation obtained with the two filters is discussed and illustrated for 2100 systems: the dependence upon separation and magnitude difference between components is clearly and quantitatively shown.

The new site testing survey in the Canary Islands' Observatories

The future establishment of large telescopes at the Observatorio del Roque de los Muchachos (ORM) has raised the necessity of designing a site-testing campaign, aimed specifically at selecting their emplacements, as well as characterizing correctly the local seeing behaviour and the fluctuations of the turbulent field in the area covered by the observatory.

Fried's parameter derived from observations of granulation outside the disk centre

A new method has recently been developed to obtain the Fried's parameter from observations of granulation outsude the disk centre, based on the different degradation suffered by the images on the directions parallel and perpendicular to the solar limb, due to the geometrical foreshortening. This procedure has been applied to CCD images obtained at the Swedish Solar Tower of the Observatorio del Roque de los Muchachos, with satisfactory results which are presented and discussed.

Photometry and spectroscopy of the solar granulation along the polar axis and equator

From high-resolution CCD images of granulation obtained at the Swedish Solar Tower of the Observatorio del Roque de los Muchachos at different positions on the solar disk, mean bi-dimensional spatial power spectra have been obtained at each position and restored following the method proposed by Rodriguez Hidalgoet al. (1990). The variation with latitude of the power spectrum, of the granular brightness contrast and of the mean wave number of the power spectrum are presented. The analysis is completed with spectroscopic observations obtained at the Gregory Coude Telescope of the Observatorio del Teide. The centre-to-limb and latitudinal variation of the bisectors, residual intensities and equivalent widths are shown for several photometric lines.

Ultraviolet to near-infrared continuum flux distribution in the active binary RS canum venaticorum

We present multifrequency observations of the active binary RS CVn. Ultraviolet observations were obtained from the IUE data bank. Optical observations were made at the Observatorio del Roque de los Muchachos (La Palma), while the infrared observations were obtained at the Observatorio del Teide (Tenerife).

CCD TIME-RESOLVED PHOTOMETRY OF FAINT CATACLYSMIC VARIABLES. III.

ABSTRACT CCD time-resolved photometry in V, B, and near-IR for 17 faint cataclysmic variables (CVs) is presented and analyzed. The data are obtained at Kitt Peak National Observatory, the Perkins reflector, Lowell Observatory, and the Observatorio del Roque de los Muchachos from April-June 1989. The degree of variability and periodicities for the CVs are examined. It is observed that the variability of most of the stars is consistent with CV class behavior. Orbital periods for five CVs are determined, and three potential eclipsing systems are detected.

Observations of SN1988e: A mature supernova

We present the spectrum of the supernova SN1988e over the wavelength range 4750–9000 A as recorded on 11 February, 1988. The spectrum was taken in one 2000 s exposure using the Faint Object Spectrograph on the 4.2 m William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos.

Observations of SN1988A with the faint object spectrograph on the 4.2 m William Herschel Telescope

We present two spectra of the supernova SN1988A in M58 (NGC4579) over the wavelength range 4000–9700 A, as recorded by the Faint Object Spectrograph on the 4.2 m William Herschel Telescope at the Observatorio del Roque de los Muchachos. We conclude that SN1988A was a type II supernova.

The La Palma Data Archive

The Observatorio del Roque de los Muchachos is perched atop a volcanic caldera on the island of La Palma in the Canary Islands, 400 km off the coast of North Africa. Three of the telescopes at the observatory are products of a collaboration between the UK, the Netherlands, Spain and the Republic of Ireland. They are the 1.0-m Jacobus Kapteyn Telescope, the 2.5-m Isaac Newton Telescope and the 4.2-m William Herschel Telescope (which saw first light in July 1987)1. The telescopes are computer controlled (running under ADAM software), and the observations are recorded primarily in electronic form. Recognising the success of astronomical-satellite data archives, such as that generated by the International Ultraviolet Explorer, a La Palma Data Archive has been established at the Royal Greenwich Observatory. The archive will be used by astronomers wishing to exploit data obtained by other observers, by engineers interested in the performance of telescope and instruments under varying conditions, and for monitoring the way in which the telescope is used.