## Flux calibration

\label{sec:fcalib}

The FLOYDS spectra are flux calibrated using the IRAF task standard, sensfunction and calibrate. The standard frames are automatically identified from the coordinates and compared with their tabulated values. The FLOYDS spectrograph sensitivity functions have a specific shape in the second order with two deep absorptions around 3800 Å and 4400 Å (see Figs. \ref{fig:sensblue} and \ref{fig:sensblue2}). In order to reproduce this specific shape, the FLOYDS pipeline computes the sensitivity function in two steps: a first step with the full second order range (3000-6000 Å) is fitted with a low order function (usually 10-12), and a second step is focused on a smaller window with a higher order in order to reproduce the two deep absorptions. The two blue sensitivity functions are then merged into a single sensitivity function. Because of this, specific standards with a dense and wide coverage of tabulated flux are required. The standard stars that are usually used for FLOYDS are reported in Table \ref{tab:specphotstandards}.

The 2D frames (2df) after being flux and wavelength calibrated have the following units: $$10^{-20}$$ erg cm$$^{-2}$$ s$$^{-1}$$ Å$$^{-1}$$

FLOYDS Spectrophotometric Standard Stars\label{tab:specphotstandards}
Standard Name RA (FK5, J2000) DEC (FK5, J2000) Proper motion (mas/yr) V mag Sp. Type Instrument
GD71 05 52 27.614 15 53 13.75 85, $$-$$174 13.032 DA1 FTS/FTN
LTT 3218 08 41 32.50 $$-$$32 56 34.0 $$-$$1031.7, 1354.3 11.85 DA5 FTS
GD153 12 57 02.337 22 01 52.68 $$-$$46, $$-$$204 13.35 DA1.5 FTN
BD+28d4211 21 51 11.07 28 51 51.8 10.47 FTN
BD+75d325 08 10 49.31 74 57 57.5 9.51 FTN
Feige34 10 39 36.71 43 06 10.1 11.12 FTN
G191-B2B 05 05 30.6 52 49 54 11.781 FTN
HZ43 13 16 22.0 29 05 57 12.914 FTN
EG274 16 23 33.837 $$-$$39 13 46.16 76.19, 0.96 11.029 DA2 FTS
EG131 19 20 34.923 $$-$$07 40 00.07 $$-$$60.87, $$-$$162.15 12.29 DBQA5 FTS
LTT 7379 18 36 25.941 $$-$$44 18 36.93 $$-$$177.05, $$-$$160.31 10.22 G0 FTS
LTT 7989 20 11 12.08 $$-$$36 06 06.5 522, $$-$$1691 11.5 M5V FTS
Feige110 23 19 58.398 $$-$$05 09 56.16 $$-$$10.68, 0.31 11.5 sdO FTS/FTN