GAPS: Using the information of the HARPS-N exposure-meter to improve the precision of RV measurements
Date Issued
2013
Author(s)
Abstract
While taking a spectrum, if the flux received from the detector is not equally time-distributed while the shutter is open, the Radial Velocity (RV) information we receive can’t be exactly referred to the middle of the exposure. That’s why last generation spectrographs use the information of an exposure-meter to measure the centroid of the flux received vs. time, to correct the time information in case of a change in the seeing conditions during the exposure.
The HARPS-N reduction pipeline does not take into account, up to now, the exposure-meter information, using by default the mid-exposure time as the reference value for each exposure.
If the information of the exposure-meter centroid in the fits files of HARPS-N (keyword ‘HIERARC EXP_METER_A EXP CENTROID’) is reliable and trustworthy, it’s not difficult to include it in the analysis of the radial velocities (even if it’s not always present). The problem is to correct for the Barycentric Earth Radial Velocity (BERV) at the relative time, in a homogeneous way to the HARPS-N pipeline.
With the correction of the BERV at the right time, we can insert the information of the exposure- meter centroid in the RVs estimation of the pipeline, where available.
Volume
GAPS-SCI-REP-0006
Rights
open.access
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2013_GAPS-SCI-REP-006-expmeter-0.2.pdf
Description
GAPS: report exposure-meter
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300.62 KB
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Adobe PDF
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