The multifunction photoelectric photometer of Torino Observatory

The paper describes the design and the realization of a multiple-function photoelectric photometer made by Trieste Observatory for Torino Observatory. The system design shows a two-beam, sequential multiband photon counting and analog photoelectric photometer configuration based on a PDP8/E computer for the control and data acquisition and elaboration. The actual realization of the system and the use of it in the one-beam configuration operating now at torino Observatory shows the advantages of such a solution and the easiness in modifying and determining the system functions by software programs rather than by hardware specials. Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. The realization of the machine was fully supported by Torino Observatory. Trieste Observatory-Instruments and Data Processing Group (5/76).     

Estimate of the optimum measuring time in the synchronous photometry of optical sources

The note shows how to estimate accurately the optimum measuring time in the measurement of a periodical optical source by means of a synchronous photometer affected by phase-tracking error. The procedure used can be easily generalized to sources or signal patterns not considered here. The optimum number of scans to be averaged results to be typicallyN _opt≈0.5r/ɛ for an optical source of Lorentzian signal pattern, wherer is the duty cycle of the pulsed component and ɛ the relative truncation error of the local sync to the source period. Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. Trieste Observatory — Instruments and Data Processing Group (4/76).     

Explosion of Comet 17P/Holmes as revealed by the Spitzer Space Telescope

An explosion on Comet 17P/Holmes occurred on 2007 October 23, projecting particulate debris of a wide range of sizes into the interplanetary medium. We observed the comet using the mid-Infrared Spectrograph (5-40 μm), on 2007 November 10 and 2008 February 27, and the imaging photometer (24 and 70 μm), on 2008 March 13, on board the Spitzer Space Telescope. The 2007 November 10 spectral mapping revealed spatially diffuse emission with detailed mineralogical features, primarily from small crystalline olivine grains. The 2008 February 27 spectra, and the central core of the 2007 November 10 spectral map, reveal nearly featureless spectra, due to much larger grains that were ejected from the nucleus more slowly. Optical images were obtained on multiple dates spanning 2007 October 27-2008 March 10 at the Holloway Comet Observatory and 1.5-m telescope at Palomar Observatory. The images and spectra can be segmented into three components: (1) a hemispherical shell fully 28′ on the sky in 2008 March, due to the fastest (262 m s⁻¹), smallest (2 μm) debris, with a mass ; (2) a ‘blob’ or ‘pseudonucleus’ offset from the true nucleus and subtending some 10′ on the sky, due to intermediate speed (93 m s⁻¹) and size (8 μm) particles, with a total mass ; and (3) a ‘core’ centered on the nucleus due to slower (9 m s⁻¹), larger (200 μm) ejecta, with a total mass . This decomposition of the mid-infrared observations can also explain the temporal evolution of the millimeter-wave flux. The orientation of the leading edge of the ejecta shell and the ejecta ‘blob,’ relative to the nucleus, do not change as the orientation of the Sun changes; instead, the configuration was imprinted by the orientation of the initial explosion. The distribution and speed of ejecta implies an explosion in a conical pattern directed approximately in the solar direction on the date of explosion. The kinetic energy of the ejecta >10²¹ erg is greater than the gravitational binding energy of the nucleus. We model the explosion as being due to crystallization and release of volatiles from interior amorphous ice within a subsurface cavity; once the pressure in the cavity exceeded the surface strength, the material above the cavity was propelled from the comet. The size of the cavity and the tensile strength of the upper layer of the nucleus are constrained by the observed properties of the ejecta; tensile strengths on >10 m scale must be greater than 10 kPa (or else the ejecta energy exceeds the binding energy of the nucleus) and they are plausibly 200 kPa. The appearance of the 2007 outburst is similar to that witnessed in 1892, but the 1892 explosion was less energetic by a factor of about 20.     

Evidence for an Extended Extragalactic Gamma Ray Source

High energy gammay–ray emission from an extended region between the squasars 3C273 and 3C279 in Virgo has been detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory(CGRO). This emission shows a remarkably constant flux over an observation time of years between June 1991 and December 1993. The data analysis shows, that the structure is not the result of an instrumental effect. The object has a perfect power law photon spectrum with index α=-2.06 ± 0.05 which is different from the spectra of the neighboring quasars 3C273 and 3C279. Integration of the spectrum leads to a flux estimation of (7.0± 0.3) × 10^-7 γ cm^-2s^-1 above 100 MeV. No galactic or extragalactic counterpart is found at other wavelengths. Indications point, however, at an extragalactic origin of the gamma radiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The digital system ARTEMIS for real-time processing of radio transient emissions in the solar corona

We present the real-time digital data processing system named ARTEMIS that was developed and constructed by the Space Research Department (DESPA) of Paris-Meudon Observatory to digitize, calibrate, format, date, process, compress, and archive in real time signals from multichannel receivers. This system is controlled by a multiprocessor computer based on Motorola MC 68010/68020 processors; it permits the automatic, routine recording of 128 parallel channels at a rate up to 300 samples per second and per channel with a 12-bit accuracy (4096 levels of intensity); it is used to process and record the 120 channels of a multichannel solar radiospectrograph in the frequency range 110–469 MHz; the remaining 8 channels are used for a scanning spectrograph in the frequency range 30–80 MHz and a two-dimensional multicorrelator interferometer at 75.5 MHz. The large quantity of raw data is reduced in real-time from about 1.3 Gbytes to about 40 Mbytes per day by the use of an original algorithm for real-time data compression. It is expected that this new facility will allow us to build a very large data base of digitized and accurately calibrated solar events, in order to achieve statistical measurements over long periods of time.     

Automated astrographic plates measuring process

The astrographic plates measuring process applied at the Astronomical Observatory of Valencia has been described.The measure of astrographic plates of our minor planets observation programme has been carried out by means of a binocular microscope with a photometer, held by a personal computer through an interface. The process of measure in each position of the plate holder is automated, once two stars are selected and the sequence of the objects to be measured is defined.The process will be improved in the next future, by the substitution of the searching device (a photometer) by a CCD camera plus a digitizer board.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Characteristics of Light Scattering at Small Phase Angles by Surfaces Consisting of Spherical Particles

We present the results of measurements of the phase dependences of brightness and of the polarization and depolarization characteristics for surfaces consisting of spherical glass particles in the phase-angle range from 0.1° to 5.0°. The measurements are performed using the laboratory photometer/polarimeter of Kharkov Astronomical Observatory and the photometer of Jet Propulsion Laboratory. An optically thick layer of transparent-glass spheres with mean size of about 57 m and refractive index of 1.44 exhibits a strong opposition effect due to single scattering. The contribution of interparticle scattering is nearly independent of the phase angle. At an angle of 0.4°, the spheres exhibit a glory ring that manifests itself in the phase behavior of all characteristics investigated. Small details are seen on the curves when a monochromatic radiation source is used for measurements. Their occurrence is confirmed by calculations based on the Mie theory. The unusual behavior of the phase dependences of reflectivity, degree of polarization, and color index for layers composed of spherical particles can be used to search for sites of possible deposits of spherical glass (or ice) particles in regoliths of atmosphereless celestial bodies.     

Mineralogy and thermal properties of V-type Asteroid 956 Elisa: Evidence for diogenitic material from the Spitzer IRS (5-35 μm) spectrum

We present the thermal infrared (5-35 μm) spectrum of 956 Elisa as measured by the Spitzer Infrared Spectrograph (“IRS”; Houck, J.R. et al. [2004]. Astrophys. J. Suppl. 154, 18-24) together with new groundbased lightcurve data and near-IR spectra. From the visible lightcurve photometry, we determine a rotation period of 16.494 ± 0.001 h, identify the rotational phase of the Spitzer observations, and estimate the visible absolute magnitude (H_V) at that rotational phase to be 12.58 ± 0.04. From radiometric analysis of the thermal flux spectrum, we find that at the time of observation 956 Elisa had a projected radius of 5.3 ± 0.4 km with a visible albedo p_V = 0.142 ± 0.022, significantly lower than that of the prototype V-type asteroid, 4 Vesta. (This corresponds to a radius of 5.2 ± 0.4 km at lightcurve mean.) Analysis with the standard thermal model (STM) results in a sub-solar temperature of 292.3 ±  2.8 K and beaming parameter η = 1.16 ± 0.05. Thermophysical modeling places a lower limit of on the thermal inertia of the asteroid’s surface layer (if the surface is very smooth) but more likely values fall between 30 and depending on the sense of rotation.The emissivity spectrum, calculated by dividing the measured thermal flux spectrum by the modeled thermal continuum, exhibits mineralogically interpretable spectral features within the 9-12 μm reststrahlen band, the 15-16.5 μm Si-O-Si stretching region, and the 16-25 μm reststrahlen region that are consistent with pyroxene of diogenitic composition: extant diogenitic pyroxenes fall within the narrow compositional range Wo_2±1En_74±2Fs_24±1. Spectral deconvolution of the 9-12 μm reststrahlen features indicates that up to ≈20% olivine may also be present, suggesting an olivine-diogenite-like mineralogy. The mid-IR spectrum is inconsistent with non-cumulate eucrite as the major component on the surface of 956 Elisa, although cumulate eucrite material may be present at abundances lower than that of the diogenite component.Analysis of new near-IR spectra of 956 Elisa with the Modified Gaussian Model (MGM; Sunshine, J.M., Pieters, C.M., Pratt, S.F. [1990]. J. Geophys. Res. 95 (May), 6955-6966) results in two pyroxene compositions: 75% magnesian low-Ca pyroxene and 25% high-Ca pyroxene. High-Ca pyroxene is not evident in the mid-IR data, but may belong to a component that is underrepresented in the mid-IR spectrum either because of its spatial distribution on the asteroid or because of its particle size. High-Ca pyroxenes that occur as exsolution lamellae may also be more evident spectrally in the NIR than in the mid-IR. In any case, we find that the mid-IR spectrum of 956 Elisa is dominated by emission from material of diogenite-like composition, which has very rarely been observed among asteroids.     

The spectrum of ɛ Aurigae outside eclipse

The identification, the equivalent widths, the profiles and the radial velocities as deduced from 18 spectra of Aurigae are presented and discussed.The observations have been made at the Astronomical Observatory of Haute Provence (CNRS). This work has been partially supported by a contract of Consiglio Nazionale delle Ricerche (CNR).     

Power spectra of Hα Doppler shifts

The temporal characteristics of the chromospheric velocity field in a quiet region are studied by means of a carefully guided sequence of 215 H spectra of the disk centre lasting 54 min. The Doppler shifts of each frame at = 0.4 Å are measured and the velocity history of each position on the sun is reconstructed. The velocity power spectrum is found for each of 256 points along the total slit length of 280000 km.A steady downward velocity is associated with places where the amplitude of the fluctuating velocity is high. The average velocity power spectrum exhibits three main features: (1) A peak at 287 sec, (2) A group of high frequency peaks in the range 150–210 sec, and (3) A low frequency peak with a period of 900 sec.The relationship of these features to the Ca K network is discussed.Member of the High Altitude Observatory Solar Project at Sacramento Peak, on leave from Dunsink Observatory, Ireland.     

A search for 5 min periodic structure in solar 2 cm emission

Two hundred and eighty-five hours of solar data obtained from the University of Iowa 2 cm radiometer during 1968–1969 were analyzed for evidence of periodic structure related to the 5 min periodic chromospheric oscillations detected in optical line emissions. A power spectral analysis of the data failed to show any statistically significant (> 96 % confidence) periodic activity in the frequency range 1–15 mHz (periods of 1–16 min) for data organized according to solar activity in H, soft solar X-rays (2–12 ), and several microwave frequencies (3–15 GHz).A small shift in power from low to higher frequencies in the power spectrum of the 2 cm data was found to be correlated with H and X-ray activity. This power shift is attributed to a relative increase in chromospheric turbulence at altitudes common to H, X-ray, and 2 cm emission.Consistent statistical analyses of previous works reporting evidence for oscillations at microwave and extreme-ultraviolet frequencies indicate that confidence in these previous results is marginal.A model for chromospheric oscillation bursts in quiescent supergranules is incorporated into a statistical analysis of the power spectrum detectability of the oscillations to understand the negative results obtained.     

Venus wind map at cloud top level with the MTR/THEMIS visible spectrometer, I: Instrumental performance and first results

Solar light gets scattered at cloud top level in Venus’ atmosphere, in the visible range, which corresponds to the altitude of 67 km. We present Doppler velocity measurements performed with the high resolution spectrometer MTR of the Solar telescope THEMIS (Teide Observatory, Canary Island) on the sodium D2 solar line . Observations lasted only 49 min because of cloudy weather. However, we could assess the instrumental velocity sensitivity, per pixel of 1 arcsec, and give a value of the amplitude of zonal wind at equator at .     

R-band light curve of Comet 9P/Tempel 1 during the Deep Impact event

We present high-speed CCD photometry of Comet 9P/Tempel 1 during the Deep Impact event on 2005 July 4 UT. Approximately 2 h and 50 min of R-band data were acquired at Mount Laguna Observatory with a temporal resolution of 5.5 s. The flux increased by 9% in the first minute after impact. This was followed by a more gradual two-part linear rise, with a change in slope at 9.2 min post-impact, at which time the rate of brightening increased from ∼ to ∼. An analysis of the light curve obtained with the guide camera on the United Kingdom Infrared Telescope and yields very similar results. These findings are mildly in disagreement with the 3-part linear rise found by Fernández et al. (2007) in that we do not find any evidence for a change at 4 min post-impact. We interpret the linear rise phase as due to solar illumination of the edge of an expanding optically thick dust ejecta plume. After approximately 20 min, the light curves begin to flatten out, perhaps coincident with the start of the transition to becoming optically thin. In the large apertures (>10^″) the light curve continues to gradually rise until the end of the observations. In smaller apertures, the light curves reach a peak at approximately 50 min, then decrease back towards the pre-impact flux level. The drop in flux in the smaller apertures may be caused by the ejecta expanding beyond the edge of the photometric aperture, and if so, we can use this timescale to infer an expansion velocity of ∼, consistent with previous published estimates.     

Clustering of Emerging Magnetic Flux

We report observations of the large-scale spatial dependence of the Sun's luminosity variations over the period 1993–1995. The measurements were made using a new scanning disk solar photometer at Big Bear Solar Observatory, specially designed to measure large-scale brightness variations at the 10^–4 level. Since the level of solar activity was very low for the entire observation period, the data show little solar cycle variation. However, the residual brightness signal I/I (after subtracting the mean, first, and second harmonics) does show a strong dependence on heliocentric angle, peaking near the limb. This is as one would expect if the residual brightness signal (including the excess brightness coming from the active latitudes) were primarily facular in origin. Additional data over the next few years, covering the period from solar minimum to maximum, should unambiguously reveal the large-scale spatial structure of the solar cycle luminosity variations.     

Spectroscopic study of the supergiant star 6 Cassiopeiae

Twenty-five coudé spectrograms (22 with dispersion 12 Å mm^–1 and three 7 Å mm^–1) of 6 Cassiopeiae (A3 Ia) have been studied. The observations were made at the Haute Provence Observatory. The results of the analysis suggest a correlation between the variations of the equivalent widths, the microturbulence and the radial velocity. The radial velocity and turbulent velocity present a rapid variation with time, even in intervals as short as about an hour. The hydrogen lines are slightly asymmetric but the strongest Feii lines are clearly asymmetric. We found that the amount of asymmetry of the strongest Feii lines (I>6) correlates with the loggf value, with the estimated laboratory intensityI, and with the equivalent widthW .The observations have been made at the Astronomical Observatory of Haute Provence (CNRS). This work has been supported by TUBITAK (Scientific and Technical Research Council of Turkey), and partially by CNR (Consiglio Nazionale delle Ricerche) of Italy.     

An investigation of Pluto’s troposphere using stellar occultation light curves and an atmospheric radiative-conductive-convective model

We use a radiative-conductive-convective model to assess the height of Pluto’s troposphere, as well as surface pressure and surface radius, from stellar occultation data from the years 1988, 2002, and 2006. The height of the troposphere, if it exists, is less than 1 km for all years analyzed. Pluto has at most a planetary boundary layer and not a troposphere. As in previous analyses of Pluto occultation light curves, we find that the surface pressure is increasing with time, assuming that latitude and longitude variations in Pluto’s atmosphere are negligible. The surface pressure is found to be slightly higher ( μbar in 1988,  μbar in 2002, and 18.5 ± 4.7 μbar in 2006) than in our previous analyses with the troposphere excluded. The surface radius is determined to be . Comparison of the minimum reduced chi-squared values between the best-fit radiative-conductive-convective (i.e., troposphere-included) model and best-fit radiative-conductive (i.e., troposphere-excluded) shows that the troposphere-included model is only a slightly better fit to the data for all 3 years. Uncertainties in the small-scale physical processes of Pluto’s lower atmosphere and consequently the functional form of the model troposphere lend more confidence to the troposphere-excluded results.     

Mars high resolution gravity fields from MRO, Mars seasonal gravity, and other dynamical parameters

With 2 years of tracking data collection from the MRO spacecraft, there is noticeable improvement in the high frequency portion of the spherical harmonic Mars gravity field. The new JPL Mars gravity fields, MRO110B and MRO110B2, show resolution near degree 90. Additional years of MGS and Mars Odyssey tracking data result in improvement for the seasonal gravity changes which compares well to global circulation models and Odyssey neutron data and Mars rotation and precession (). Once atmospheric dust is accounted for in the spacecraft solar pressure model, solutions for Mars solar tide are consistent between data sets and show slightly larger values (k₂ = 0.164 ± 0.009, after correction for atmospheric tide) compared to previous results, further constraining core models. An additional 4 years of Mars range data improves the Mars ephemeris, determines 21 asteroid masses and bounds solar mass loss (dGM_Sun/dt < 1.6 × 10⁻¹³ GM_Sun year⁻¹).     

Spectroscopic and photometric detection of interacting processes and their evolution in the eclipsing binary TX UMa

Nearly one century of spectroscopic and photometric observations of eclipsing binary TX UMa offer a good opportunity for studying evolutionary processes in this system. Extensive spectroscopic observations carried out with the D.A.O. high-dispersion spectrographs in 1969–70 and at the Ondejov Observatory in 1972–80 cover all radial velocity curve with particular emphasis on phases within primary minimum of the light curve. The manifestations of interacting processes as well as the presence of the spectrum of secondary component are examined in the ever changing line spectra. Photometric observations having been collected at the Skalnaté Pleso Observatory since 1966 display orbital period changes. Evolution of period changes using this photometric material in connection with the published data is presented.     

Helium 10830 Å measurements of the Sun

Measurements of the Sun in the near-infrared He i 10830 Å absorption line were performed using the echelle spectrograph with a dispersion of 6.71 mÅ per pixel at the Vacuum Tower Telescope (German Solar Telescopes, Teide Observatory, Izaña, Tenerife, Spain) on May 26, 1993. These measurements were compared with full-disc soft X-ray images of the Sun (Japanese solar satellite Yohkoh), full-disc solar images in H (Big Bear Solar Observatory), full-disc solar images in the He i 10830 Å line (National Solar Observatory, Kitt Peak) and with full-disc microwave solar maps at 37 GHz (Metsähovi Radio Research Station). In the He 10830 Å line the Sun displays a limb darkening similar to that in the visible part of the spectrum. Active regions and H filaments show a strong absorption in the He 10830 Å line, whereas the absorption is weak in coronal holes.