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Spectral Templates

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Spectral templates (usually late type stars) are required for the analysis of kinematical data on external galaxies (or other stellar ensembles). In the near-IR, the most commonly used features are the CO overtone bands at λ > 2.3µm. Although observational and theoretical libraries exist at lower spectral resolutions (R<3000), no comprehensive set of stellar kinematic templates was available to be used with two of the configurations of Gemini NIR instruments used for stellar population kinematic studies in external galaxies - NIFS and GNIRS 111 l/mm grating (both longslit and IFU) - and all programmes using those configurations would invariably spend some science time taking a small set of stellar spectra to use as templates. This led to a constant duplication of data taking, since those targets are programme calibrations and are not made available to other users until the end of the default 18 months proprietary period.

During period 2006B at Gemini South, given the unusually poor conditions over the whole semester, and the eventual end of true "poor weather" programmes in the queue, a Director's Discretionary "poor weather" GS-2006B-DD-3 programme was carried out to provide the NIR community with a larger set of late (F7 to M3 types I, II, III and V) stellar spectra, with intermediate S/N (30-50), including the four CO overtone bands (2.24-2.42µm) at R~6000 resolution. A subset of the targets was also observed at a slightly bluer spectral range to improve usefulness for NIFS users, overlapping with the red setting on the first two CO bands.

To the original sample of 29 stars observed with GNIRS, another 31 were added from NIFS observations obtained as part of programmes GN-2006A-SV-123, GN-2006B-Q-107, GN-2007A-Q-25, and from archived public data (from programmes GN-2006A-C-11, GN-2007A-Q-45 and GN-2007A-Q-62), covering the full range 2.1 to 2.5µm at a similar resolution.

A separate R~18000 spectral template library is also available.

Detailed description of the observations, data reduction, template usage and systematic effects related to differences in resolution, the range of CO band equivalent width spanned by the templates, and further analysis in the "template mismatch" issue, can be found in "The Gemini Spectral Library of Near-IR Late-Type Stellar Templates and Its Application for Velocity Dispersion Measurements". Winge, Cláudia; Riffel, Rogemar; Storchi-Bergmann, Thaisa, 2009, ApJS, 185, 186.

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Library Description

GNIRS sample (at Gemini South)
Instrument configuration
GNIRS IFU + 111 l/mm grating in the K band
"Red" setting
λc=2.335µm (2.24-2.43µm), dλ=1.84Å/pixel
"Blue" setting
λc= 2.245µm (2.15-2.33µm), dλ=1.85Å/pixel
Combined spectrum
2.15-2.43µm, rebinned to dλ = 1Å/pixel
Observed sample
29 objects in the "red" setting, from F7III to M3III
Of these, 23 objects were also observed in the "blue" setting
NIFS sample 1 (v1.5)
Instrument configuration
NIFS IFU + K grating + HK filter, 3.0arcsec or KG3+ND masks
Original sampling
λc=2.20 and 2.25µm (2.07-2.47µm), dλ=2.13Å/pixel
Observed sample
3 objects centred at 2.20µm, 8 centred at 2.25µm, spectral types from G8II to M5III
NIFS sample 2 (v2.0)
Instrument configuration
NIFS IFU + K grating + HK filter, 3.0arcsec or KG3+ND masks
Original sampling
λc=2.20 (2.04-2.43µm), dλ=2.13Å/pixel
Observed sample
Spectral types from G8III to M3I

The GNIRS sample

The observed sample was selected from a list kindly provided by Greg Doppmann, compiled from the literature (mostly based in Cayrel de Strobel et al 1997), and the selection was based exclusively on observability: targets which were visible for as long as possible during the 06B semester, bright enough to provide the desired S/N on a reasonable on-source time under CC=90, IQ=ANY conditions, and having a hot (A0-A7) star close enough (and bright enough!) to be used for telluric correction. The fact that both target and telluric stars also had to have a bright (V<13mag) guide star available as well, restricted even more the choices.

The observing conditions also determined the instrument configuration: to achieve R=5900 with GNIRS in long slit mode, one would have to use the 0.30" slit - implying in very large slit losses under IQ=Any (FWHM>0.80" in K) seeing. Given the superior performance of the original GNIRS IFU in the K band (over 90% of that of the equivalent long slit mode), there was only a small loss in sensitivity by using the IFU+111 l/mm grating configuration.

The NIFS sample 1 (V1.5):

The data were obtained either as programme calibrations for GN-2006A-SV-123 and GN-2007A-Q-25, and therefore based solely in observability and brightness; or as part of another "poor weather" programme GN-2006B-Q-107, and in this case following the same rationale as the GNIRS sample (bright enough for poor conditions, with proper telluric and guide stars available). The stars observed as part of N06A-SV-123 and N07A-Q-25 used the AOWFS for guiding, while for N06B-Q-107, the AO fold was parked and guiding was done using the PWFS2.

The NIFS sample 2 (V2.0):

This extra set was derived from archived public data, originally obtained for programmes GN-2006A-C-11, GN-2007A-Q-45 and GN-2007A-Q-62, retrieved and processed by M. R. Diniz, as part of an undergraduate research project at the Universidade Federal de Santa Maria, in Brazil (with R. Riffel as supervisor).

All the GNIRS data collected under programme GS-2006B-DD-3 has been made public from the start in the Gemini Science Archive. The NIFS data were subject to the standard proprietary period. This page contains links to the table of final processed spectra. Details on the data reduction, template usage and systematic effect, can be found in the paper cited above. The community at large is welcome to download all or part of the library as needed, and users of GNIRS or NIFS are encouraged to explore its use as an alternative to requesting further observation of spectral standards with their science programmes. If the raw data are re-processed to be used in papers or publications, please use the standard Gemini acknowledgement text and the above programme IDs. For the processed data contained in this page, the authors would appreciate acknowledgement of the library use (Winge, Riffel and Storchi-Bergmann, 2009).

The data are presented in standard FITS format, and the user can select either the GNIRS red (2.24-2.42µm) or blue (2.15-2.32µm) spectral ranges at their native spectral binning; or the combined spectrum (when available), rebinned to 1 Å/pix. The NIFS spectra are also presented at native binning and rebinned to 1 Å/pix.

The authors would like to thank the former Gemini Deputy Director and Head of Science, Jean-Rene Roy, and the former Gemini South Head of Science Operations, Michael West, for the support and time allocation for our GNIRS programme. Many thanks as well to all the Gemini South observers and SSAs that so positively believed that no conditions were ever too poor to give GS-2006B-DD-3 a chance!

Current release is Version 2.0 - Additional NIFS data included.

History and release notes:

2012 Jun 25 - Version 2.0 uploaded to the Gemini Web Site - this corresponds to additional templates observed with NIFS, retrieved from the Gemini Science Archive. No changes made to the already existing spectra (GNIRS and NIFS sample 1). All files include full headers, and the data have been corrected to rest wavelength.

2009 Jan 31 - Version 1.5 uploaded to the Gemini Web Site

  • Highlights
    • NIFS data added!
    • Complete headers from the last step of reduction before extracting the spectra to 1-D added back to all spectra.
    • Continuum shape removal improved prior to combining the GNIRS settings.
    • Final spectra are corrected to rest velocity. This was done by taking a strong, isolated line at 2.2814µm and using that as a reference point to all the remaining spectra. The procedure allowed for correcting in one step the intrinsic radial velocity and any zero-point offset that could remain from the wavelength calibration.

2007 Apr 10 - Version 1.0 uploaded to the Gemini Web Site.

  • Highlights and ToDo list
    • The "blue" setting spectral range currently starts at 2.18µm. After tinkering with the telluric correction for a while, I'm still not satisfied with the result in the Brγ region.
    • The image headers are NOT complete. The original GNIRS files are MEF, so most of the information is located in the primary header unit (extension [0]), and gets lost when the spectrum is extracted. This is also in the list for the next release.
    • Final spectra are:
      • NOT flux calibrated. The continuum shape has been removed by fitting a low order polynomial. I decided to go this way rather than tackle the issue of flux calibrating the spectra for this release.
      • NOT corrected for Galactic extinction.
      • NOT corrected for heliocentric radial velocity.
    • Error vectors (variance planes) NOT included. This is admittedly important for a good evaluation of the errors in the cross-correlation results, but the variance planes are not being propagated correctly through the reduction process.

Last update 2014 February 03; Cláudia Winge

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