31 research outputs found
Herschel SPIRE Fourier Transform Spectrometer: Calibration of its Bright-source Mode
The Fourier Transform Spectrometer (FTS) of the Spectral and Photometric
Imaging REceiver (SPIRE) on board the ESA Herschel Space Observatory has two
detector setting modes: (a) a nominal mode, which is optimized for observing
moderately bright to faint astronomical targets, and (b) a bright-source mode
recommended for sources significantly brighter than 500 Jy, within the SPIRE
FTS bandwidth of 446.7-1544 GHz (or 194-671 microns in wavelength), which
employs a reduced detector responsivity and out-of-phase analog signal
amplifier/demodulator. We address in detail the calibration issues unique to
the bright-source mode, describe the integration of the bright-mode data
processing into the existing pipeline for the nominal mode, and show that the
flux calibration accuracy of the bright-source mode is generally within 2% of
that of the nominal mode, and that the bright-source mode is 3 to 4 times less
sensitive than the nominal mode.Comment: 15 pages, 16 figures, accepted for publication in Experimental
Astronom
Observing Extended Sources with the \Herschel SPIRE Fourier Transform Spectrometer
The Spectral and Photometric Imaging Receiver (SPIRE) on the European Space
Agency's Herschel Space Observatory utilizes a pioneering design for its
imaging spectrometer in the form of a Fourier Transform Spectrometer (FTS). The
standard FTS data reduction and calibration schemes are aimed at objects with
either a spatial extent much larger than the beam size or a source that can be
approximated as a point source within the beam. However, when sources are of
intermediate spatial extent, neither of these calibrations schemes is
appropriate and both the spatial response of the instrument and the source's
light profile must be taken into account and the coupling between them
explicitly derived. To that end, we derive the necessary corrections using an
observed spectrum of a fully extended source with the beam profile and the
source's light profile taken into account. We apply the derived correction to
several observations of planets and compare the corrected spectra with their
spectral models to study the beam coupling efficiency of the instrument in the
case of partially extended sources. We find that we can apply these correction
factors for sources with angular sizes up to \theta_{D} ~ 17". We demonstrate
how the angular size of an extended source can be estimated using the
difference between the sub-spectra observed at the overlap bandwidth of the two
frequency channels in the spectrometer, at 959<\nu<989 GHz. Using this
technique on an observation of Saturn, we estimate a size of 17.2", which is 3%
larger than its true size on the day of observation. Finally, we show the
results of the correction applied on observations of a nearby galaxy, M82, and
the compact core of a Galactic molecular cloud, Sgr B2.Comment: Accepted for publication by A&
First results from Herschel-SPIRE performance tests
The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments on the European Space Agency's Herschel mission. At the start of 2004 the Cryogenic Qualification Model (CQM) of SPIRE was tested with the aim of verifying the instrument system design and evaluating key performance parameters. We present a description of the test facility, an overview of the instrument tests carried out on the CQM, and the first results from the analysis of the test data. Instrument optical efficiency and detector noise levels are close to the values expected from unit-level tests, and the SPIRE instrument system works well, with no degradation in performance from stray light, electromagnetic interference or microphonically induced noise. Some anomalies and imperfections in the instrument performance, test set-up, and test procedures have been identified and will be addressed in the next test campaign
Plasma Composition Measurements in an Active Region from Solar Orbiter/SPICE and Hinode/EIS
A key goal of the Solar Orbiter mission is to connect elemental abundance measurements of the solar wind enveloping the spacecraft with extreme-UV (EUV) spectroscopic observations of their solar sources, but this is not an easy exercise. Observations from previous missions have revealed a highly complex picture of spatial and temporal variations of elemental abundances in the solar corona. We have used coordinated observations from Hinode and Solar Orbiter to attempt new abundance measurements with the Spectral Imaging of the Coronal Environment (SPICE) instrument, and benchmark them against standard analyses from the EUV Imaging Spectrometer (EIS). We use observations of several solar features in active region (AR) 12781 taken from an Earth-facing view by EIS on 2020 November 10, and SPICE data obtained one week later on 2020 November 17, when the AR had rotated into the Solar Orbiter field of view. We identify a range of spectral lines that are useful for determining the transition region and low-coronal-temperature structure with SPICE, and demonstrate that SPICE measurements are able to differentiate between photospheric and coronal magnesium/neon abundances. The combination of SPICE and EIS is able to establish the atmospheric composition structure of a fan loop/outflow area at the AR edge. We also discuss the problem of resolving the degree of elemental fractionation with SPICE, which is more challenging without further constraints on the temperature structure, and comment on what that can tell us about the sources of the solar wind and solar energetic particles
Slow Solar Wind Connection Science during Solar Orbiterâs First Close Perihelion Passage
The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilize the extensive suite of remote-sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote-sensing and in situ measurements of slow wind originating at openâclosed magnetic field boundaries. The SOOP ran just prior to Solar Orbiterâs first close perihelion passage during two remote-sensing windows (RSW1 and RSW2) between 2022 March 3â6 and 2022 March 17â22, while Solar Orbiter was at respective heliocentric distances of 0.55â0.51 and 0.38â0.34 au from the Sun. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low-latency in situ data and full-disk remote-sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Postobservation analysis using the magnetic connectivity tool, along with in situ measurements from MAG and SWA/PAS, showed that slow solar wind originating from two out of three of the target regions arrived at the spacecraft with velocities between âŒ210 and 600 km sâ1. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter
Shock wave propagation in the atmosphere of a variable star
Imperial Users onl
Far-infrared spectroscopy of the giant planets: measurements of ammonia and phosphine at Jupiter and Saturn and the continuum of Neptune
International audienceWe detected rotational transition features of ammonia and phosphine in the far-infrared spectra of Jupiter and Saturn and measured the far-infrared continuum of Neptune with high photometric accuracy. These observations were made with the long-wavelength spectrometer (LWS) aboard the infrared space observatory (ISO). The LWS covered the wavelength region between 43 and 197 mum (51-233 cm -1) with both medium and high spectral resolving power. Also Neptune's continuum was measured with the LWS and at shorter wavelengths with the ISO short-wavelength spectrometer (SWS). The spectra observed in the far-infrared are compared to synthetic spectra calculated from atmospheric radiative transfer models using expected values for the constituent vertical concentration profiles