SPIRE point source photometry: within the Herschel interactive processing environment (HIPE)

The different algorithms appropriate for point source photometry on data from the SPIRE instrument on-board the Herschel Space Observatory, within the Herschel Interactive Processing Environment (HIPE) are compared. Point source photometry of a large ensemble of standard calibration stars and dark sky observations is carried out using the 4 major methods within HIPE: SUSSEXtractor, DAOphot, the SPIRE Timeline Fitter and simple Aperture Photometry. Colour corrections and effective beam areas as a function of the assumed source spectral index are also included to produce a large number of photometric measurements per individual target, in each of the 3 SPIRE bands (250, 350, 500μm), to examine both the accuracy and repeatability of each of the 4 algorithms. It is concluded that for flux densities down to the level of 30mJy that the SPIRE Timeline Fitter is the method of choice. However, at least in the 250 and 350μm bands, all 4 methods provide photometric repeatability better than a few percent down to at approximately 100mJy. The DAOphot method appears in many cases to have a systematic offset of ～8 % in all SPIRE bands which may be indicative of a sub-optimal aperture correction. In general, aperture photometry is the least reliable method, i.e. largest scatter between observations, especially in the longest wavelength band. At the faintest fluxes, <30mJy, SUSSEXtractor or DAOphot provide a better alternative to the Timeline Fitter.     

Relative pointing offset analysis of calibration targets with repeated observations with Herschel-SPIRE Fourier-transform spectrometer

We present a method to derive the relative pointing offsets for SPIRE Fourier-Transform Spectrometer (FTS) solar system object (SSO) calibration targets, which were observed regularly throughout the Herschel mission. We construct ratios R _obs(ν) of the spectra for all observations of a given source with respect to a reference. The reference observation is selected iteratively to be the one with the highest observed continuum. Assuming that any pointing offset leads to an overall shift of the continuum level, then these R _obs(ν) represent the relative flux loss due to mispointing. The mispointing effects are more pronounced for a smaller beam, so we consider only the FTS short wavelength array (SSW, 958–1546 GHz) to derive a pointing correction. We obtain the relative pointing offset by comparing R _obs(ν) to a grid of expected losses for a model source at different distances from the centre of the beam, under the assumption that the SSW FTS beam can be well approximated by a Gaussian. In order to avoid dependency on the point source flux conversion, which uses a particular observation of Uranus, we use extended source flux calibrated spectra to construct R _obs(ν) for the SSOs. In order to account for continuum variability, due to the changing distance from the Herschel telescope, the SSO ratios are normalised by the expected model ratios for the corresponding observing epoch. We confirm the accuracy of the derived pointing offset by comparing the results with a number of control observations, where the actual pointing of Herschel is known with good precision. Using the method we derived pointing offsets for repeated observations of Uranus (including observations centred on off-axis detectors), Neptune, Ceres and NGC 7027. The results are used to validate and improve the point-source flux calibration of the FTS.     

Herschel SPIRE FTS relative spectral response calibration

Herschel/SPIRE Fourier transform spectrometer (FTS) observations contain emission from both the Herschel Telescope and the SPIRE Instrument itself, both of which are typically orders of magnitude greater than the emission from the astronomical source, and must be removed in order to recover the source spectrum. The effects of the Herschel Telescope and the SPIRE Instrument are removed during data reduction using relative spectral response calibration curves and emission models. We present the evolution of the methods used to derive the relative spectral response calibration curves for the SPIRE FTS. The relationship between the calibration curves and the ultimate sensitivity of calibrated SPIRE FTS data is discussed and the results from the derivation methods are compared. These comparisons show that the latest derivation methods result in calibration curves that impart a factor of between 2 and 100 less noise to the overall error budget, which results in calibrated spectra for individual observations whose noise is reduced by a factor of 2–3, with a gain in the overall spectral sensitivity of 23 % and 21 % for the two detector bands, respectively.     

Uncovering the Bias in Low-Degree p-Mode Linewidth Fitting

Obtaining reliable estimates of linewidths in the power spectra of low-degree p modes is problematic at low frequency. In this regime, the mode coherence time increases with decreasing frequency, often causing the modes to be unresolved in relatively long duration spectra. The signal-to-noise ratio is also less favourable at low frequency, resulting in fits to power spectra underestimating the true linewidth of the p modes owing to the tails of the Lorentzian peaks becoming dominated by the background noise. We use a numerical simulation approach to assess the effect of this bias on the fitted widths of p-mode peaks and calculate observational duration limits required to obtain an unbiased estimate of the p-mode linewidth as a function of frequency. This is done in four different cases, where the precision of the artificial data is set at 0.25, 0.50, 0.75, and 1.00 m?s^?1 by adding random?scatter to increase the sample standard deviation per 40-second measurement. In all cases, the observational duration required to accurately obtain width estimates increases beyond that required for sufficient spectral resolution below a certain threshold frequency. For modes at ≈?1500 μHz, with an amplitude of approximately ten times the background, observations of up to 972 days are required to obtain an unbiased estimate of the linewidth. This is equivalent to ≈?18 times the coherence time of the corresponding p modes.     

Herschel SPIRE FTS telescope model correction

Emission from the Herschel telescope is the dominant source of radiation for the majority of SPIRE Fourier transform spectrometer (FTS) observations, despite the exceptionally low emissivity of the primary and secondary mirrors. Accurate modelling and removal of the telescope contribution is, therefore, an important and challenging aspect of FTS calibration and data reduction pipeline. A dust-contaminated telescope model with time invariant mirror emissivity was adopted before the Herschel launch. However, measured FTS spectra show a clear evolution of the telescope contribution over the mission and strong need for a correction to the standard telescope model in order to reduce residual background (of up to 7 Jy) in the final data products. Systematic changes in observations of dark sky, taken over the course of the mission, provide a measure of the evolution between observed telescope emission and the telescope model. These dark sky observations have been used to derive a time dependent correction to the telescope emissivity that reduces the systematic error in the continuum of the final FTS spectra to ～0.35 Jy.     

Enhanced X-ray emission above 50 keV in sco X-1

Balloon observations of the X-ray source Sco X-1 carried out in November 1978 have revealed a thermal spectrum withkT?7 keV in the 20–60 keV energy band. In addition, there was evidence of a high energy component, possibly variable, above ～50 keV. The spectral form of this component could not be determined but was hard with a 60 keV flux of ～10^?4 photons (keV cm² s)^?1.     

The upper Jovian atmosphere aerosol content determined from a satellite eclipse observation

The Galilean satellite eclipse technique for measuring the aerosol distribution in the upper Jovian atmosphere is described and applied using 30 color observations of the 13 May 1972 eclipse of Ganymede obtained with the 5-m Hale telescope. This event probes the South Temperate Zone. The observed aerosol lies above the visible cloud tops, is very tenuous and varies with altitude, increasing rapidly with downward passage through the tropopause. The aerosol extinction coefficient, κ_a (λ1.05 μm), is ～1.1 × 10^?9 cm^?1 in the lower stratosphere and ～1.1 × 10^?8 cm^?1 at the tropopause. The 1σ uncertainty in these values does not exceed 50% The observations require some aerosol above the tropopause but do not clearly determine its structure. The present analysis emphasizes an extended haze distribution, but the alternate possibility is not excluded that the stratospheric aerosol resides in a thin layer. The aerosol extinction increases with decreasing wavelength and indicates the particle radius to be ?0.2 μm. Larger radii are impossible. These overall results confirm Axel's (1972) suggestion of a small quantity of dust above the Jovian cloud tops and the optical depths are consistent with those required to explain the low uv albedo.     

High precision radial velocities with GIANO spectra

Radial velocities (RV) measured from near-infrared (NIR) spectra are a potentially excellent tool to search for extrasolar planets around cool or active stars. High resolution infrared (IR) spectrographs now available are reaching the high precision of visible instruments, with a constant improvement over time. GIANO is an infrared echelle spectrograph at the Telescopio Nazionale Galileo (TNG) and it is a powerful tool to provide high resolution spectra for accurate RV measurements of exoplanets and for chemical and dynamical studies of stellar or extragalactic objects. No other high spectral resolution IR instrument has GIANO’s capability to cover the entire NIR wavelength range (0.95-2.45 μm) in a single exposure. In this paper we describe the ensemble of procedures that we have developed to measure high precision RVs on GIANO spectra acquired during the Science Verification (SV) run, using the telluric lines as wavelength reference. We used the Cross Correlation Function (CCF) method to determine the velocity for both the star and the telluric lines. For this purpose, we constructed two suitable digital masks that include about 2000 stellar lines, and a similar number of telluric lines. The method is applied to various targets with different spectral type, from K2V to M8 stars. We reached different precisions mainly depending on the H-magnitudes: for H ～ 5 we obtain an rms scatter of ～ 10 m s^?1, while for H ～ 9 the standard deviation increases to ～ 50 ÷ 80 m s^?1. The corresponding theoretical error expectations are ～ 4 m s^?1 and 30 m s^?1, respectively. Finally we provide the RVs measured with our procedure for the targets observed during GIANO Science Verification.     

The minimum masses of black holes from the generalized uncertainty principle and the uncertainty principle

In this paper we compare the minimum masses of Schwarzschild black hole obtained from the generalized uncertainty principle and the Heisenberg uncertainty principle. Three minimum masses are obtained. The first two are the order of Planck mass which can be normally accepted. The last one based on Scardigli’s hypothesis and consideration is about M _c ?10¹⁵ g～10²⁰ M _pl which may be problematic. Whether right or wrong, it needs the astronomical observations.     

Optical variability of the radio source Z0524+03

The results of photometric observations of the optical component of the known variable radio source Z0524+03 are reported. The light variations amounted to 1.5 ^m during the period from January 21, 1998 to January 28, 2001 and occurred synchronously in the BVRI bands on time scales ranging from several years to 0.05 days. The spectral index of the object (S ～ ν ^α) varied from ?2.4 to ?1.3 from minimum to maximum light.Polarimetric observations made on January 22/23, 1999 showed that the linear polarization of the radiation of the object did not exceed 1% at the time of observation.Three local-standard candidates have been selected in the field of the object.     

AOST: Fourier spectrometer for studying mars and phobos

An AOST Fourier spectrometer of the Phobos-Soil project is intended for studying Mars and Phobos by means of measurements of IR radiation spectra of the Martian surface and atmosphere, the Phobos surface, and the spectrum of solar radiation passing through the Martian atmosphere on its limb. The main scientific problems to be solved with the spectrometer on Mars are measurements of methane content, search for minor constituents, and study of diurnal variations in the temperature and atmospheric aerosol. The spectrometer will also study the Martian and Phobos surface both remotely and after landing. The spectral range of the instrument is 2.5?C25 ??m, the best spectral resolution (without apodization) is 0.6 cm^?1, and the instantaneous field of view is 2.5°. The recording time of one spectrum is equal to 5 s in solar observations and 50 s in observations of Mars and Phobos. The instrument has self-thermal stabilization and two-axis pointing systems, as well as a built-in radiation source for flight calibration. The spectrometer mass is 4 kg, and power consumption is up to 13 W. Scientific problems, measurement modes, and, briefly, engineering implementation of the experiment are discussed in this work.     

Infrared photometry of Nova Delphini 2013 (=V339 Del) in the first sixty days after its outburst

The results of JHKLM photometry for Nova Delphini 2013 obtained in the first sixty days after its outburst are analyzed. Analysis of the energy distribution in a wide spectral range (0.36–5 µm) has shown that the source mimics the emission of normal supergiants of spectral types B5 and A0 for two dates near its optical brightness maximum, August 15.94 UT and August 16.86 UT, respectively. The distance to the nova has been estimated to be D ≈ 3 kpc. For these dates, the following parameters have been estimated: the source’s bolometric fluxes ～9 × 10^?7 and ～7.2 × 10^?7 erg s^?1 cm^?2, luminosities L ≈ 2.5 × 10⁵ L _⊙ and ≈2 × 10⁵ L _⊙, and radii R ≈ 6.3 × 10¹² and ≈1.2 × 10¹³ cm. The nova’s expansion velocity near its optical brightness maximum was ～700 km s^?1. An infrared (IR) excess associated with the formation of a dust shell is shown to have appeared in the energy distribution one month after the optical brightness maximum. The parameters of the dust component have been estimated for two dates of observations, JD2456557.28 (September 21, 2013) and JD2456577.18 (October 11, 2013). For these dates, the dust shell parameters have been estimated: the color temperatures ≈1500 and ≈1200 K, radii ≈6.5 × 10¹³ and 1.7 × 10¹⁴ cm, luminosities ～4 × 10³ L _⊙ and ～1.1 × 10⁴ L _⊙, and the dust mass ～1.6 × 10²⁴ and ～10²⁵ g. The total mass of the material ejected in twenty days (gas + dust) could reach ～1.1 × 10^?6 M _⊙. The rate of dust supply to the nova shell was ～8 × 10^?8 M _⊙ yr^?1. The expansion velocity of the dust shell was about 600 km s^?1.     

Pulsations in the eclipsing variable system AS Camelopardalis

We performed photoelectric observations of AS Cam in 2002–2004. Five new times of minima were obtained. Their positions are consistent with the previously found light equation for the system and with the hypothesis that the difference between the observed (15°/100 yr) and theoretical (44°/100 yr) rates of apsidal motion results from the presence of a third body in the system. A Fourier analysis of two observational data sets, 1968–1970 and 2002–2004, reveals, with a high significance, periodic light variations with a frequency of ω ₀ = 1.0950 ± 0.0001d^?1 and an amplitude of ～0 _. ^m 020, which are probably caused by the radial pulsations of one of the components. We found a seasonal phase shift of these oscillations that may be produced by other periodic processes in the system. We show that the fairly large scatter of observed times of minima about the theoretical curve of the light equation can be explained by the presence of pulsations. Using the 2002 and 2004 observations as an example, we show that including the pulsations reduces this scatter.     

Laboratory studies of the HNCO molecular spectrum for precise spectroscopy of dark clouds

Detailed studies of the internal motions of dark clouds using spectral lines of many molecules require a laboratory frequency accuracy of the order of a few m s^?1. Based on our laboratory studies of the HNCO rotational spectrum in the ground vibrational state, we have increased significantly the accuracy of frequency calculation in a wide range of quantum numbers. We have achieved an (1σ) uncertainty for rotational transitions in the K _a = 0, 1 states recalculated to the Doppler velocity scale ≤2 m s^?1 for all frequencies <1.1 THz. This value allows radio-astronomical measurements with an accuracy comparable to that of the highest-precision observations based on spectral lines of other molecules.     

Comparison between infrared Martian disk spectra and optical properties of terrestrial analogs

Medium spectral resolution (20 cm^?1) infrared measurements of the Martian disk made between 2900 and 5600 cm^?1 from the NASA Lear Airborne Observatory have been successfully compared with predictions derived from a model of the Martian soil and atmosphere. Modeling of the Martian atmosphere permitted the extraction of Martian soil reflectance in the CO₂ bands centered at 3657 cm^?1. Three previously considered acceptable Martian soil analogs, limonite, montmorillonite, and basalt, were analyzed to determine the optical complex indices of refraction in the same range as the airborne observations, for mathematical modeling. A characteristic surface particle size ～1 to 3 μm diameter is indicated. It is concluded that the Martian soil surface near-infrared optical properties are consistent with a soil composition similar to montmorillonite or limonite, mixed with a basalt.     

W Ursae Majoris stars: Period-spectral type relation and period changes

The relation between period and spectral type is examined for 33 W Ursae Majoris stars for which accurate observations have enabled us to clearly classify their eclipse types at the primary minimum (transit (A) or occultation (W)). About a half of the examined stars are of A-type, and the rest correspond to W-type. Periods of W-type systems are found to fall within 0.25–0.5 days, while periods of A-type systems range between 0.25–0.9 days. For A-type systems certain period-spectral type relations seem to hold, but for W-type systems no definite relation could be found. Statistically, a W Ursae Majoris star will undergo a period change every ～17000 cycles, on the average, and a time scale for the period change (d lnP/dt)^?1 is estimated to be about 10⁶ years.     

AKARI: space infrared cooled telescope

AKARI, formerly known as ASTRO-F, is the second Japanese space mission to perform infrared astronomical observations. AKARI was launched on 21 February 2006 (UT) and brought into a sun-synchronous polar orbit at an altitude of 700 km by a JAXA M-V rocket. AKARI has a telescope with a primary-mirror aperture size of 685 mm together with two focal-plane instruments on board: the Infrared Camera (IRC), which covers the spectral range 2–26 μm and the Far-Infrared Surveyor (FIS), which operates in the range 50–180 μm. The telescope mirrors are made of sandwich-type silicon carbide, specially developed for AKARI. The focal-plane instruments and the telescope are cooled by a unique cryogenic system that kept the telescope at 6K for 550 days with 180 l super-fluid liquid Helium (LHe) with the help of mechanical coolers on board. Despite the small telescope size, the cold environment and the state-of-the-art detectors enable very sensitive observations at infrared wavelengths. To take advantage of the characteristics of the sun-synchronous polar orbit, AKARI performed an all-sky survey during the LHe holding period in four far-infrared bands with FIS and two mid-infrared bands with IRC, which surpasses the IRAS survey made in 1983 in sensitivity, spatial resolution, and spectral coverage. AKARI also made over 5,000 pointing observations at given targets in the sky for approximately 10 min each, for deep imaging and spectroscopy from 2 to 180 μm during the LHe holding period. The LHe ran out on 26 August 2007, since which date the telescope and instrument are still kept around 40K by the mechanical cooler on board, and near-infrared imaging and spectroscopic observations with IRC are now being continued in pointing mode.     

Luminosity-HI velocity width relation for spirals

Multicolour and multiaperture photometry of 22 late-type Virgo cluster galaxies in a newV (5500 Å),r (6738 Å),IV (10500 Å) system confirm the previously known correlations between the luminosity and H₁ velocity width, and show them to be strongly wavelength dependent with the slope of the relation reaching a maximum value of ～ ? 10 at 10500 Å and remaining constant at longer wavelengths. The scatter in the luminosity-H₁ width relation is nearly the same, whether we use (V)^c _?0.5, (r)^c _?0.5, (IV)^c _-0.5, or (H)^c _-0.5 magnitudes. The error in the determination of the corrected magnitudes is much less than the scatter in the luminosity-H₁ width relations as evidenced by the fact that the residuals of individual galaxies inV, r, IV, andH are correlated with one another. An attempt to use a ‘kinematic magnitude’ instead of an isophotal magnitude shows the slope of the luminosity-H₁ width relations to be reduced substantially. Observations in theV, r, andIV system for fifteen field galaxies and three galaxies in the Cancer and Zw 74-23 clusters have been obtained and combined with the H₁ velocity width to derive their differences in distance modulus, between the galaxy and the Virgo cluster, through the luminosity-H₁ width relations of the Virgo cluster galaxies. The three independent differences in the distance modulus of each galaxy agree with one another indicating that the relations usingV, r andIV magnitudes have the same zero point in absolute magnitude, independent of the wavelength of observations. The distance modulus difference from the Virgo cluster to the three galaxies U 4334, U 8942 and U 8944, which are outside the Local Supercluster, are +1·50, +3·45 and +2·81 mag respectively and are in agreement with those of +1·75, +3·23 and +2·46 mag derived for the same galaxies by Aaronsonet al. (1980) throughH magnitudes. The scatter in the velocity distance relation of the field galaxies compares well with the mean error derived in the luminosity-H_I width relations and hence is intrinsic.     

Saturn's rings: Particle size distributions for thin layer models

The small physical thickness of Saturn's rings requires that radio occultation observations be interpreted using scattering models with limited amounts of multiple scatter. A new model in which the possible order of near-forward scatter is strictly limited allows for the small physical thickness, and can be used to relate Voyager 1 observations of 3.6-and 13-cm wavelength microwave scatter from Saturn's rings to the ring particle size distribution function n(a), for particles with radius 0.001 ≤ a ≤ 20 m. This limited-scatter model yields solutions for particle size distribution functions for eight regions in Saturn's rings, which exhibit approximately inverse-cubic power-law behavior, with large-size cutoffs in particle radius ranging from about 5 m in ring C to about 10 m in parts of ring A. The power-law index is about 3.1 in ring C, about 2.8 in the Cassini division, and increases systematically with radial location in ring A from 2.7 at 2.10R_s to slightly more than 3.0 at 2.24R_s. Corresponding mass densities are 32–43 kg/m² in ring C, 188 kg/m² in the Cassini division, and 244–344 kg/m² in ring A, under the assumption that the material density of the particles is 0.9 g/cm³. These values are a factor of 1 to 2 lower than first-order mass loading estimates derived from resonance phenomena. In view of the uncertainties in the measurements and in the linear density wave model, and the strong arguments for icy particles with specific gravity not greater than about 1, we interpret this discrepancy as being indicative of possible differences in the regions studied, or systematic errors in the interpretation of the scattering results, the density wave phenomena, or some combination of the above.     

Symbiotic halo star LT Del: Phase variations of the emission spectrum and parameters of the cool component

Long-term photometric and spectroscopic observations of the yellow symbiotic star LT Del are analyzed. UBV light curves are presented. Based on the observations of 20 cycles, we have refined the orbital period of the star, P = 476 _· ^d 0 ± 1 _· ^d 0. The brightness has been found to be unstable at some orbital phases with an amplitude up to 0 _· ^m 3. We have measured the fluxes in hydrogen and helium emission lines and in continuum and investigated their relationship to the orbital period. The fluxes in hydrogen and HeI lines follow the UBV light curves in phase; the He II 4686 Å flux does not depend on the phase and is constant within the accuracy of our measurements. The intensity ratio of the 4686 Å andHβ lines changes from 0.2 to 0.9 over the period. We interpret the spectroscopic observations based on the hypothesis of heating and ionization of the stellar wind from a cool component by high-frequency radiation from a hot star with a temperature of 105 K. We have estimated the spectral type of the cool star from our photometry and its continuum energy distribution as a bright K2–4 red giant branch halo star. The bolometric luminosity and mass loss rate have been estimated for the K component to be L _bol ～ 700L _⊙ and \(\dot{M}\) ～ 10^?8 M _⊙ yr^?1, respectively.