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Instrument Upgrades: Small Project Examples

 

We provide here a few examples of possible projects for our Instrument Upgrades Small Projects Program. These projects are just meant to illustrate a large range of scope possible for these projects. Although you are welcome to propose for one of these example projects, we encourage you to use your own experiences and propose projects that you find particularly interesting and relevant for your scientific objectives. We selected a few simple examples to demonstrate that each project should produce a tangible result in the form of a new capability added to the instrument suite when the project is concluded.

Instrument
 Upgrade option
GNIRS / NIFS
Commissioning of a NIR OIWFS
NIFS
GPOL commissioning with NIFS
GMOS-N / S
GMOS low resolution blue grating
GMOS-S
Commissioning of Hamamatsu’s frame transfer mode
Flamingos-2
Medium band filters for F2








 

 

Commission a NIR OIWFS

Both Gemini North NIR spectrographs are currently used with the peripheral wavefront sensor (PWFS), which is an optical guider and requires stars located at large radii to avoid vignetting.  Commissioning of the on-instrument wavefront sensor (OIWFS) would enable new science targets and increase the viability of the highest spectroscopic resolution modes in GNIRS and the highest spatial resolution modes in NIFS. For instance, the availability of a NIR OIWFS will benefit the study of:

i) Young stellar objects and proto-binaries, which are deeply embedded in nearby molecular clouds. Such clouds block out background stars for guiding, or tip-tilt stars in the case of adaptive optics.

ii) Large clusters near the Galactic Center or on the Galactic plane, which are hidden behind high extinction zones in the plane.

iii) Active galactic nuclei and starburst galaxies, also can suffer from high extinction and in several cases do not have tip-tilt stars available for adaptive optics.

For the specific case of GNIRS, the narrowest slits (0.1”-0.3”) observations presently require re-acquisitions every hour of observation due to the relative flexure of the focal plane mask and the PWFS.  The GNIRS OIWFS was never commissioned, it has a NIR detector, 3 arcmin patrol FOV, and would allow to expand the sky coverage of the instrument to regions of high optical obscuration.  Using guiding stars nearer than 4 arcminutes from the science target will minimize the flux losses due to flexure and the telescope time used in re-acquisitions.  GNIRS OIWFS could also expand Altair’s LGS sky coverage when supporting high resolution spectroscopy, which is presently strongly limited by its WFS patrol field (R<30”).

 

Similarly, NIFS faint sources observation is also compromised by the relative flexure between the PWFS and the IFU, which precludes deep exposures or the combination of many exposures without a bright source to register the relative positions. For non-AO guiding mode for NIFS uses the PWFS, which precludes the use of guiding stars nearer than 3.8 arcminutes. The NIFS + ALTAIR (NGS) + OIWFS system, with a field of view of 2 arcminutes would be especially useful when taking observations with a bright star centered behind an occulting disk and with science observations requiring long exposures (>∼300sec) to avoid smearing of the image by flexure during the integration.  

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GPOL commissioning with NIFS

Commissioning one of the polarisation modulators which are already available at the Observatory, used with NIFS, GMOS and other instrument suited for this kind of observations would enable new scientific niches by providing a polarimetry capability to Gemini:

i) It has been recently proposed that there is an AGN fundamental plane spanned by two independent axis: orientation and the properties of the clumps in the putative torus along the line of sight. Spectropolarimetry detection of scattered radiation is still a strong tool to test the models that explains type 1 and 2 AGN’s as a single kind of object, as well as the ones that propose some type 2 AGNs being evolutionary precursors of type 1.

ii) Star-formation scenarios:  it has been argued that massive star formation is initially regulated by the magnetic field, which is eventually overwhelmed by the star formation process. Spectropolarimetry studies allow to better understanding the role and interplay of the newly formed massive stars, bipolar outflows, the hot ionized gas and interstellar dust grains, and the magnetic fields in these regions.

iii) Asteroid surfaces:  spectropolarimetry can be used as a remote sensing tool in addition to traditional reflectance methods. Recent studies indicate that objects with marginally different relative reflectance spectra may have very different polarization spectra. The relationships between wavelength variation of linear polarization and the properties of surfaces, including albedo and composition would provide a stronger classification scheme.

The polarisation modulator GPOL units are already available at the observatory and are capable of working from 0.4 to 5 μm. The GN GPOL assembly is presently installed and could be made operational with an instrument located at the bottom of the A&G.  Afterwards it would be easy to commission its use with other instruments:  NIRI, GMOS and GNIRS had in their baseline designs Wollaston prisms for use with GPOL.

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GMOS low resolution blue grating

GMOS instruments have a set of gratings, which allow assorted spectral coverages and resolutions across the optical range.  However, nebular spectroscopy would be strongly benefited from a setup allowing to observe all diagnostic-relevant optical emission lines with a single grating setting. The physical conditions and abundances of star formation regions, AGN’s, late stellar evolution ejections and warm interstellar medium can all be well characterized with a minimum coverage from the [OII]3727 lines to the [SII]6731. In order to allow some deblending of the emission lines, a sampling of 0.1 nm/pixel is necessary, which for the 0.5 arcsec slit yields resolutions in the range 5000-10000.  With GMOS+E2V detectors two gratings are required to do this.


Designing, purchasing and commissioning a grating would give coverage from about 360nm to 820nm at ~0.075 nm/pix, considering the Hamamatsu pixel size. The optimal blaze wavelength is approximately 525nm. The extended red end will allow full optical nebular lines coverage in a sample of objects with redshifts in the range 0-0.2.  Similarly, a change in the grating angle would allow performing multi-object spectroscopy at higher redshifts with a simultaneous coverage of 0.1-0.2 in redshift space.

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Commission the frame transfer mode in the Hamamatsu CCD’s

GMOS-S new Hamamatsu CCD’s have the capability of being read in frame transfer mode. The possibility of reading faster the detector and at a higher frequency time sampling would benefit solar system atmosphere occultation studies, stellar atmosphere pulsations and flares, accretion disks flickering, contact binary phenomena, planetary transits and other similar time-series phenomena.


This mode is based in the transfer of charge collected during an exposure to an unexposed region of the detector, allowing for an immediate start of the next exposure. The Hamamatsu CCD’s can allow 100% duty cycle time series with integration times as low as a few to ten seconds, with the lower limit imposed by the detector controller electronics, which has a minimum allowable exposure time of 1 second.  Hamamatsu documentation includes the information about the necessary clock settings to engage this readout mode.


The upgrade requires also the installation of a focal plane mask which blocks the part of the detector frame area that would be used for transfer.

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Medium band filters to F2

Flamingos-2 currently has standard broad band filters and JH/HK order sorting filters, plus an extended K band filter for spectroscopy purposes.  Designing band-passes and procuring filters to split either the J or the K band would enable new science niches.  The large FOV of F2 complements the large aperture of the telescope, making it suitable for medium band color surveys for mapping high-redshift clusters, improving stellar population studies in nearby galaxies, and deep surveys of the young and proto-stellar objects in galactic star forming complexes.

With the largest FOV of any NIR instrument at Gemini, F2 is also the natural candidate for deep photometric redshift searches. 
F2 has the possibility of adding two filters to the regular set Y,J,H,Ks,JH,HK. Custom medium-band filters could split the J or K bands, depending on the relative scientific advantages of each option. The filters must be designed, procured and commissioned.

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