Teide Observatory Research Articles

High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere

We present the results of 8 yr of infrared photometric monitoring of a large sample of stars visible from Teide Observatory (Tenerife, Canary Islands). The final archive is made up of 10,949 photometric measures through a standard InSb single-channel photometer system, principally in JHK, although some stars have measures in L'. The core of this list of stars is the standard-star list developed for the Carlos Sánchez Telescope. A total of 298 stars have been observed on at least two occasions on a system carefully linked to the zero point defined by Vega. We present high-precision photometry for these stars. The median uncertainty in magnitude for stars with a minimum of four observations and thus reliable statistics ranges from 0.0038 mag in J to 0.0033 mag in K. Many of these stars are faint enough to be observable with array detectors (42 are K > 8) and thus to permit a linkage of the bright and faint infrared photometric systems. We also present photometry of an additional 25 stars for which the original measures are no longer available, plus photometry in L' and/or M of 36 stars from the main list. We calculate the mean infrared colors of main-sequence stars from A0 V to K5 V and show that the locus of the H-K color is linearly correlated with J-H. The rms dispersion in the correlation between J-H and H-K is 0.0073 mag. We use the relationship to interpolate colors for all subclasses from A0 V to K5 V. We find that K and M main-sequence and giant stars can be separated on the color-color diagram with high-precision near-infrared photometry and thus that photometry can allow us to identify potential mistakes in luminosity class classification.

Behaviour of Comet 21P/Giacobini-Zinner during the 1998 perihelion

Comet 21P/Giacobini–Zinner was observed from Nov. 8 to Dec. 10, 1998. Pre- and post-perihelion CCD images of the gas (CN, C2 ) and dust (green and red continua) coma were obtained with the 82 cm IAC-80 telescope at Teide Observatory (Canary Islands, Spain). For and (i.e. characteristic of HCN being the CN parent species), the CN column density profiles are best reproduced with parent and daughter lifetimes of the order of 19 300 and 256 000 s. An equally good reproduction of the observed profiles is achieved by considering that a mixture of nitrogen compounds expanding at and with a lifetime of 19 000 s produces CN with an ejection velocity of and a lifetime of 174 000 s. Fitting the observed CN profiles with variable velocities and lifetimes, the results indicate that the nature of the CN precursor in comet 21P/Giacobini–Zinner is still unclear, ruling out HCN as the only precursor and favouring a mixture of nitrogen compounds. Regarding C2 , the derived lifetimes are 35 000 and 62 000 s, if the parent and daughter velocities are fixed at ∼ 1 . Gas production rates derived by means of the Vectorial modeling with the mentioned above lifetimes and velocities indicate that (i) the comet activity decreases with decreasing r H (i.e. peak activity is not reached at the perihelion), and (ii) as already known, the comet is typically depleted in C2 with a . The azimuthally averaged surface brightness profiles of the continuum images are well fitted with in a representation at projected radial distances (ρ ) larger than 1000 km. The continuum light scattered from the dust in the coma of comet Giacobini–Zinner is redder than the Sun light on every date from Nov. 8 to 24, regardless the cometocentric distance. On Nov. 25, there is a sudden change in the dust color, being considerably bluer than the Sun, whereas on Dec. 7 and 8, the dust became much redder than it was before. These color variations do not seem to be related to sudden variations (relative minimum or maximum) in the cometary activity. The gas-to-dust mass ratio is ∼ 1, but affected by a large uncertainty (about a factor of 2) since the comet was not simultaneously imaged in the OH band, and the H2 O production rate has been considered from other measurements taken some weeks before ours.

Multiple delays in QSO 0957+561: observational evidence and interpretation

Q0957+561A,B is a double-imaged quasar that has been intensively observed during the last 10 yr in different optical bands and with several telescopes, and we concentrated on recent public data obtained at the Apache Point Observatory (APO) and the Teide Observatory (TO). When an intrinsic event appears in the light curve of Q0957+561A, its twin event (a similar feature) is seen in the brightness record of Q0957+561B, and thus, one can measure the corresponding time delay. The TO data set includes two prominent twin events, which were detected with a time separation of 425 ± 4 d. On the other hand, from the APO data set, we found a clear evidence for two different time delays associated with two pairs of twin events: 417.0 ± 0.6 (APO main twin events) and 432.0 ± 1.9 d (APO secondary twin events), where the APO (main)–APO (secondary) difference delay is of −15 ± 2 d. In agreement with Yonehara's idea, if the three pairs of twin events are originated inside a standard hybrid source (accretion disc and circumnuclear stellar region), the three measured time delays indicate that they do not come from a common zone in the source. Therefore, we can consider that the prominent features are caused by flares in a standard hybrid source and discuss the size and nature of the region of flares. In this paper it is shown that the more plausible interpretation is that two of the three flares are generated at distances (from the central black hole) larger than 90 pc. Some stellar scenarios can explain the two flares far away from the black hole, while phenomena in the accretion disc cannot cause them.

Adaptive optics and multi-conjugate adaptive optics with the VTT

We are currently developing adaptive optics (AO) system with a multi-conjugate extension for the German solar vacuum tower telescope (VTT) at the Teide Observatory on Tenerife.Multi-conjugate adaptive optics (MCAO) is a technique for increasing the field of view by compensating atmospheric turbulence along several, adjacent lines of sight. A conventional AO system compensates only a single line of sight in the direction of the lock point of its wavefront sensor. At larger field angles, the light from the source transverses higher layers of turbulence which are not sampled by the conventional system. Measurements at the VTT indicate that full compensation is typically restricted to a field of about 10 arcsec in diameter at visible wavelengths. An MCAO uses (at least) a second deformable mirror close to the focal plane of the telescope to compensate a larger field. The sun is a privileged target for an MCAO because the wavefront errors at larger field angles are easily measured. We intend to extend our existing AO system with a second deformable mirror and a second wavefront sensor which enables us to extend the compensated field by a factor of three in diameter.We present and discuss our concept.

GREGOR: a 1.5 m telescope for solar research

GREGOR will be a new 1.5 meter solar telescope at the Teide Observatory, Izana, Tenerife. It will provide observations with high polarimetric precision at visible and infrared wavelengths from Earth in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR replaces the 45 cm Gregory Coude telescope.

Post-focus instrumentation for GREGOR

GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coudé Telescope at the Observatorio del Teide on Tenerife. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying physical processes. GREGOR will also serve as a test bed for next generation solar telescopes. We discuss briefly the postfocus instrumentation of GREGOR.

Post-focus instrumentation for GREGOR

GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coudé Telescope at the Observatorio del Teide on Tenerife. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying physical processes. GREGOR will also serve as a test bed for next generation solar telescopes. We discuss briefly the postfocus instrumentation of GREGOR.

COSMOSOMAS: a circular scanning instrument to map the sky at centimetric wavelengths

We describe the first instrument of a cosmic microwave background experiment for mapping cosmological structures on medium angular scales (the COSMOSOMAS experiment) and diffuse Galactic emission. The instrument is located at Teide Observatory (Tenerife) and is based on a circular scanning sky strategy. It consists of a 1-Hz spinning flat mirror directing the sky radiation into a 1.8-m off-axis paraboloidal antenna, which focuses it on to a cryogenically cooled HEMT-based receiver operating in the frequency range 12–18 GHz. The signal is split by a set of three filters, allowing simultaneous observations at 13, 15 and 17 GHz, each with a 1-GHz bandpass. A 1°–5° resolution sky map complete in right ascension and covering 20° in declination is obtained each day at these frequencies. The observations presented here correspond to the first months of operation, which have provided a map of 9000 deg2 on the sky centred at Dec.=+31° with sensitivities of 140, 150 and 250 μK per beam area in the channels at 13, 15 and 17 GHz, respectively. We discuss the design and performance of the instrument, the atmospheric effects, the reliability of the data obtained and prospects of achieving a sensitivity of 30 μK per beam in 2 years of operation.

Research Note The rotation period of 804 Hispania: Some considerations on its nature

Photometric observations of 804 Hispania performed at the Teide Observatory during the opposition in September 1998 are presented and analyzed. A rotation period of 7.405 ± 0.010 h was derived. It was possible to confirm that the lightcurve presents two maxima and minima. We discuss in detail some considerations on its nature.

Infrared Imaging of Perpendicular Nested Bars in Spiral Galaxies with the Infrared Camera at the Carlos Sánchez Telescope

Images are presented of some of the galaxies in the sample of the BARS `International Time Project' in the near-infrared JHKs bands, obtained with the Infra-Red Camera at the 1.5 m Carlos Sanchez Telescope, Teide Observatory, between 1996 and 1998. We discuss the scientific importance of imaging galaxies in the near-infrared bands and recent and future developments concerning the Infra-Red Camera.

Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise?

From optical R-band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (with an overlap of about 330 d between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short time-scale events (with a duration of months), where the term ‘event’ refers to a prominent feature that may be a result of microlensing or another source of variability. Only one event lasting two weeks and rising −33 mmag was found. Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial), a smooth function plus a stationary noise process, or a correlated stationary process. Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.

The Effect of Seeing Variations in Time-Series CCD Inner Coma Photometry of Comets: A New Correction Method

Time series CCD photometry of the inner coma of active comets has been used over the last twenty years to determine the rotation period of their nucleus. Usually, the photometry is performed by using very small apertures with the aim of isolating as much as possible the brightness contribution of the nucleus with respect to the brightness of the coma or of measuring short-term gas/dust production rate diurnal variations. The effect of variations in the brightness profile of the comet and their consequences on the measured magnitude in such small apertures has never been studied before. The aim of this paper is to study this seeing effect. A series of simulated images of two comets is generated by using different values. The brightness of the simulated comets is measured by using very small apertures ranging from 2 to 16 pixels. A strong correlation between the measured magnitudes and the is found. This systematic effect can produce false variations of several tenths of magnitudes in the light curve in nights with variable conditions. A new method to correct this effect on real observations is proposed and applied to CCD observations of comets 29P/Schwassmann-Wachmann 1 and 21P/Giacobini-Zinner, carried out with the 82 cm IAC-80 Telescope at Teide Observatory (Canary Islands, Spain). The effect is clearly present in the observations, and the method is shown to be very efficient in correcting it.

Preliminary study of the evolution of solar magnetic structures and photospheric horizontal velocity fields

Abstract In October 1997, we made a coordinated observation of the solar photosphere and chromosphere at Hida observatory (Kyoto university, Japan) and at Teide observatory (Tenerife) over a 10 day. We obtained imaging data series continuously during 6 hr 45 min in G-band (4308 A) observed with the Domeless Solar Telescope (DST) at Hida on 24th October (effective FOV; 96″×99″). Additionally, in this observation, we simultaneously observed image series of the chromosphere during the latter 4 hr 10 min in H α line center and H α ±0.6 A. From these data set, we could detect that emerging flux tubes crossed the photosphere to the chromosphere and that ‘convective collapse’ phenomena appeared at the stage of the spot formation. Moreover, we confirmed that the lifetime of mesogranulation was about 4000 sec (70 min) from the temporal evolution of velocity patterns. We show here only a summary of these observations.

BVRIPhotometry of QSO 0957+561A, B: Observations, New Reduction Method, and Time Delay

CCD observations of the gravitational lens system Q0957+561A,B in the BVRI bands are presented in this paper. The observations, taken with the 82 cm IAC-80 telescope, at Teide Observatory, Spain, were made from the beginning of 1996 February to 1998 July, as part of an on-going lens monitoring program. Accurate photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component by means of DAOPHOT software. This alternative method equals and even improves the results obtained with previous techniques. The final dataset is characterized by its high degree of homogeneity as it was obtained using the same telescope and instrumentation during a period of almost 3 years. The resulting delay, obtained with a new method, the delta2-test, is of 425 +/- 4 days, slightly higher than the value previously accepted (417 days), but concordant with the results obtained by Pelt et al. (1996); Oscoz et al. (1997); Pijpers (1997); and Goicoechea et al. (1999).

A 33-GHz interferometer for cosmic microwave background observations on Tenerife

ABSTRA C T We describe a new high-sensitivity experiment for observing cosmic microwave background (CMB) anisotropies. The instrument is a two-element interferometer operating at 33 GHz with a ,3 GHz bandwidth. It is installed on the high and dry Teide Observatory site on Tenerife where successful beam-switching observations have been made at this frequency. Two realizations of the interferometer have been tested with element separations of 11.9l and 16.7l. The resulting angular resolution of ,28 was chosen to explore the amplitude of CMB structure on the large angular scale side of the Doppler (acoustic) peak. It is found that observations are unaffected by water vapour for more than 70 per cent of the time when the sensitivity is limited by the receiver noise alone. Observations over several months are expected to give an rms noise level of ,10‐20 mK covering ,100 resolution elements. Preliminary results show stable operation of the interferometer with the detection of discrete radio sources as well as the Galactic plane at Dec. aa 418 and ˇ298.

Resolution Improvement of Solar Images

A method for the improvement of resolution in an observed solar image is proposed. A blind deconvolution method is used for restoration of an atmospherically-degraded solar image, and a super-resolution method is applied to its restored image to improve the resolution. It is confirmed that a blind deconvolution process can restore fine structures that are blurred in an observed image, and that the super-resolution process can make a cutoff frequency in a blind-deconvolved image higher. A time series of super-resolved images of a sunspot observed with the 70-cm Vacuum Tower Telescope at Teide Observatory is presented.

The Rotation Period of C/1995 O1 (Hale-Bopp)

C/1995 O1 (Hale-Bopp) was observed in daylight on 16 days between 1997 April 1 and 1997 April 28, five of which had long time sequences (up to 10 hr of data), using the near infrared CAIN camera on the 1.5 m Carlos Sanchez Telescope at Teide Observatory (Tenerife, Canary Islands, Spain). Three spiral dust jet structures were observed for several almost complete rotations. A nucleus rotation period of 11.34±0.02 hr was determined from two different methods. No variations of the rotation period with time due to precessional effects were found in our data. However, the time sampling of the observations, similar to the suggested spin precession period, prevents us from ascertaining whether such variations exist. We note, though, that the good agreement of our results with the rotation periods at different epochs reported by other groups suggests that if they exist, these variations must be small, hence the rotation cannot be very complex.

Diurnal atmospheric extinction over Teide Observatory (Tenerife, Canary Islands)

Data from ve continuous years (1984 to 1989) at Teide Observatory (Iza~ na, Tenerife, Canary Islands) obtained with a full-disc solar multichannel photome- ter devoted to the detection of solar intensity oscilla- tions has now been used for a detailed study of the extinction coecient behaviour at several wavelengths (from 450 nm to 870 nm) and aerosol size distribu- tions under dierent atmospheric conditions. From this study we conclude that an extinction coecient around 0.075 mag airmass 1 at 680 nm constitutes the border- line between clear days and dusty days aected by the occasional presence of wind-blown Saharan dust. In the former the extinction can vary between 0.04 and 0.07 mag airmass 1 (at 680 nm) and in the latter between 0.075 and 0.8 mag airmass 1 (at 680 nm). Moreover the dust produces a grey eect in the wavelength range analysed in this work. From the extinction coecients we use in- version methods to compute the particle size distribution in both atmospheric conditions. Approximately, the ex- tinction on clear and dusty days is produced by aerosol particles with radius between 40 and 120 nm and between 120 and 3000 nm, respectively.

Analysis of the Difference Light Curve of the Gravitational Mirage QSO 0957+561

From optical data of Q0957+561 for 1995/1996 seasons (in the g band) and 1996/1997 seasons (in the R band) they are derived upper limits on the amplitude of the rapid microlensing fluctuations of 0.07 mag and 0.05 mag, respectively. The photometry in the R band (1996/1997 seasons) was taken at Teide Observatory (IAC-80 Telescope), Instituto de Astrofisica de Canarias, Spain. In this contribution, we also study the microlensing history (from 1981 to 1996) of the Twin QSO, which is a curious system with two optical images of similar brightness.

The Spin Axis Position of C/1995 O1 (Hale-Bopp)

Monitoring of the near-nucleus activity of C/1995 O1 (Hale-Bopp) began in Teide Observatory in August 1995. During 1996 the comet was observed on 72 nights between March 26 and November 13. A permanent fan structure was observed towards the north during the whole period of observation. The position angle of the axis of this fan was measured and its variations with time were used to determine the position of the North Pole of the cometary nucleus.