53 research outputs found
Magnetic fields in early-type stars
For several decades we have been cognizant of the presence of magnetic fields
in early-type stars, but our understanding of their magnetic properties has
recently (over the last decade) expanded due to the new generation of
high-resolution spectropolarimeters (ESPaDOnS at CFHT, Narval at TBL, HARPSpol
at ESO). The most detailed surface magnetic field maps of intermediate-mass
stars have been obtained through Doppler imaging techniques, allowing us to
probe the small-scale structure of these stars. Thanks to the effort of large
programmes (e.g. the MiMeS project), we have, for the first time, addressed key
issues regarding our understanding of the magnetic properties of massive (M > 8
M_sun) stars, whose magnetic fields were only first detected about fifteen
years ago. In this proceedings article we review the spectropolarimetric
observations and statistics derived in recent years that have formed our
general understanding of stellar magnetism in early-type stars. We also discuss
how these observations have furthered our understanding of the interactions
between the magnetic field and stellar wind, as well as the consequences and
connections of this interaction with other observed phenomena.Comment: 8 pages, 2 figures. To appear in the proceedings of the IAUS 305 -
Polarimetry: From the sun to stars and stellar environment
Magnetic Fields of Slowly Pulsating B Stars and {\beta} Cep Variables: Comparing Results from FORS1/2 and ESPaDOnS
Recently announced magnetic models for four SPB and {\beta} Cep stars, along
with magnetic detections for two additional stars, have potentially doubled the
number of known magnetic SPB and \beta Cep stars (see Grunhut et al., these
proceedings). We have reanalyzed the published data and re-reduced archival low
resolution spectropolarimetry collected with the FORS1/2 instruments at VLT on
which the models were based, and compare them with high resolution data from
the ESPaDOnS spectropolarimeter at CFHT, investigating previously noted
inconsistencies between results from the two instruments.Comment: 5 pages, 4 figures, StarPol: Stellar Polarimetry from Birth to Deat
The Wide Integral Field Infrared Spectrograph: Commissioning Results and On-sky Performance
We have recently commissioned a novel infrared ( m) integral
field spectrograph (IFS) called the Wide Integral Field Infrared Spectrograph
(WIFIS). WIFIS is a unique instrument that offers a very large field-of-view
(50 x 20) on the 2.3-meter Bok telescope at
Kitt Peak, USA for seeing-limited observations at moderate spectral resolving
power. The measured spatial sampling scale is and
its spectral resolving power is and in the
( m) and ( m) modes, respectively.
WIFIS's corresponding etendue is larger than existing near-infrared (NIR)
IFSes, which are mostly designed to work with adaptive optics systems and
therefore have very narrow fields. For this reason, this instrument is
specifically suited for studying very extended objects in the near-infrared
such as supernovae remnants, galactic star forming regions, and nearby
galaxies, which are not easily accessible by other NIR IFSes. This enables
scientific programs that were not originally possible, such as detailed surveys
of a large number of nearby galaxies or a full accounting of nucleosynthetic
yields of Milky Way supernova remnants. WIFIS is also designed to be easily
adaptable to be used with larger telescopes. In this paper, we report on the
overall performance characteristics of the instrument, which were measured
during our commissioning runs in the second half of 2017. We present
measurements of spectral resolving power, image quality, instrumental
background, and overall efficiency and sensitivity of WIFIS and compare them
with our design expectations. Finally, we present a few example observations
that demonstrate WIFIS's full capability to carry out infrared imaging
spectroscopy of extended objects, which is enabled by our custom data reduction
pipeline.Comment: Published in the Proceedings of SPIE Astronomical Telescopes and
Instrumentation 2018. 17 pages, 13 figure
The "+" for CRIRES: enabling better science at infrared wavelength and high spectral resolution at the ESO VLT
The adaptive optics (AO) assisted CRIRES instrument is an IR (0.92 - 5.2 μm) high-resolution spectrograph was in operation from 2006 to 2014 at the Very Large Telescope (VLT) observatory. CRIRES was a unique instrument, accessing a parameter space (wavelength range and spectral resolution) up to now largely uncharted. It consisted of a single-order spectrograph providing long-slit (40 arcsecond) spectroscopy with a resolving power up to R=100 000. However the setup was limited to a narrow, single-shot, spectral range of about 1/70 of the central wavelength, resulting in low observing efficiency for many scientific programmes requiring a broad spectral coverage. The CRIRES upgrade project, CRIRES+, transforms this VLT instrument into a cross-dispersed spectrograph to increase the simultaneously covered wavelength range by a factor of ten. A new and larger detector focal plane array of three Hawaii 2RG detectors with 5.3 μm cut-off wavelength will replace the existing detectors. For advanced wavelength calibration, custom-made absorption gas cells and an etalon system will be added. A spectro-polarimetric unit will allow the recording of circular and linear polarized spectra. This upgrade will be supported by dedicated data reduction software allowing the community to take full advantage of the new capabilities offered by CRIRES+. CRIRES+ has now entered its assembly and integration phase and will return with all new capabilities by the beginning of 2018 to the Very Large Telescope in Chile. This article will provide the reader with an update of the current status of the instrument as well as the remaining steps until final installation at the Paranal Observatory
Characterizing the cross dispersion reflection gratings of CRIRES+
The CRIRES+ project attempts to upgrade the CRIRES instrument into a cross dispersed Echelle spectrograph with a simultaneous recording of 8-10 diffraction orders. In order to transform the CRIRES spectrograph into a cross-dispersing instrument, a set of six reflection gratings, each one optimized for one of the wavelength bands CRIRES+ will operate in (YJHKLM), will be used as cross dispersion elements in CRIRES+. Due to the upgrade nature of the project, the choice of gratings depends on the fixed geometry of the instrument. Thus, custom made gratings would be required to achieve the ambitious design goals. Custom made gratings have the disadvantage, though, that they come at an extraordinary price and with lead times of more than 12 months. To mitigate this, a set of off-the-shelf gratings was obtained which had grating parameters very close to the ones being identified as optimal. To ensure that the rigorous specifications for CRIRES+ will be fulfilled, the CRIRES+ team started a collaboration with the Physikalisch-Technische Bundesanstalt Berlin (PTB) to characterize gratings underconditions similar to the operating conditions in CRIRES+ (angle of incidence, wavelength range). The respective test setup was designed in collaboration between PTB and the CRIRES+ consortium. The PTB provided optical radiation sources and calibrated detectors for each wavelength range. With this setup, it is possible to measure the absolute efficiency of the gratings both wavelength dependent and polarization state dependent in a wavelength range from 0.9 μm to 6 μm
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