Science Operations

Spectrophotometric Standards

MODS Primary Spectrophotometry Standards

Because MODS works from 3200 to >~10000 Angstroms, spectrophotometric standard stars with good fluxes from the UV to the near-IR are needed to adequately calibrate the data. A set of 11 stars form the preferred set of spectrophotometric standards for MODS (the “MODS primary spectrophotometric standards”).
 
The information on this page comes from the MODS website at OSU.
The MODS primary spectrophotometric standards are derived from the HST CALSPEC database and are a combination of well-observed northern hemisphere standards from the list of Oke (1990 AJ, 99, 1621) and the 4 HST white dwarf primary spectrophotometric standards of Bohlin, Colina and Findlay (1995, AJ, 100, 1316), which appear in boldface in Table 1 below.

10- and 50-Angstrom Flux Tables

For each primary standard star, flux tables with 10Å bin widths are provided. These tables are in IRAF-style ASCII 3-column format ready to be used with IRAF. Where necessary, HST stellar models or other HST calibration data were used to extend the near-IR wavelength coverage to 10500Å. These are suitable for grating-mode calibrations.

Tables with 50Å-bin widths are better suited for prism-mode calibrations and these are also provided for most of the stars. The fluxes are based on CALSPEC and the Spec50 flux tables  Massey et al (1988, ApJ 328, 315), with extensions to 1 micron from Massey and Gronwall (1990, ApJ 358, 344)

These tables have the major telluric absorption complexes censored, and the brighter stellar absorption lines have been cut out in most (but not all) tables.

The original, uncensored flux tables are available from the HST CALSPEC database.

Note that the modsIDL Reduction Pipeline uses the full CALSPEC flux tables which are included in the software distribution.


Data on the MODS Primary Spectrophotometric Standards

Useful information on the MODS primary spectrophotometric standards is provided in Table 1 below. The coordinates, proper motions, spectral type and magnitudes are from Simbad. All of these stars are roughly the same color except the redder BD+33°2642, and span about 3 magnitudes in apparent brightness. Their flux tables, at 10 angstrom and, when available also at 50 angstrom, bins are provided in the links and also in this gzipped tar file. The scripts are available on the mountain (obsN) workstations (in /home/modseng/modsScripts/modsSpecPhot/) and also can be generated from the MODS OT library.
 
Table 1: MODS Primary Spectrophotometric Standards
Star
RA
(J2000)
Dec
(J2000)
Sp Type
m(5556)
(mag)
pmRA
(mas/yr)
pmDec
(mas/yr)
t[Grating]
(sec)
t[Prism]
(sec)
Downloads
G191-B2B [1] 05:05:30.613 +52:49:51.96 DA0 11.85 +7.45 -89.54 90 10 Finder Chart
10Å Flux Table
50Å Flux Table
GD71 [2] 05:52:27.614 +15:53:13.75 DA1 13.03 +85 -174 180 30 Finder Chart
10Å Flux Table
50Å Flux Table
Feige 34 10:39:36.740 +43:06:09.26 sdO 11.25 +14.09 -25.01 120 15 Finder Chart
10Å Flux Table
50Å Flux Table
Feige 66 [3] 12:37:23.517 +25:03:59.88 sdO 10.54 +3.01 -26.05 120 15 Finder Chart
10Å Flux Table
50Å Flux Table
Feige 67 12:41:51.791 +17:31:19.76 sdO 11.89 -6.15 -36.27 120 15 Finder Chart
10Å Flux Table
50Å Flux Table
GD 153 [4] 12:57:02.337 +22:01:52:68 DA1 13.35 -46 -204 180 30 Finder Chart
10Å Flux Table
Hz 43 [5] 13:16:21.853 +29:05:55.38 DA1 12.91 -157.96 -110.23 180 30 Finder Chart
10Å Flux Table
Hz 44 13:23:35.258 +36:07:59.51 sdO 11.47 -61.6 -3.1 120 15 Finder Chart
10Å Flux Table
50Å Flux Table
BD+33 2642 15:51:59.886 +32:56:54.33 B2IV 10.80 -13.57 +0.72 120 15 Finder Chart
10Å Flux Table
BD+28 4211 [6] 21:51:11.021 +28:51:50.36 sdOp 10.56 -35.55 -58.74 60 10 Finder Chart
10Å Flux Table
50Å Flux Table
Feige 110 23:19:58.398 -05:09:56.16 sdO 11.88 -10.68 +0.31 90 10 Finder Chart
10Å Flux Table
50Å Flux Table
Notes on Individual Stars:
[1] – G191-B2B is an HST primary white dwarf star. On the finder chart it is the northernmost of the two bright stars in the field.
[2] – GD71 is an HST primary white dwarf standard stars. The NIR extension is based on HST model spectrum.
[3] – Feige 66 has only relatively low-quality near-IR extension data, and should only be used in the blue or out to about 9200Å.
[4] – GD153 is an HST primary white dwarf star. The NIR extension is based on the HST fluxes shifted by -0.02mag.
[5] – Hz 43 is an HST primary white dwarf star. The NIR extension is based on the HST model spectrum. A faint binary M-dwarf companion, Hz43B (V=14.3), is located 3-arcsec away, so this star is not recommended during poor seeing.
[6] – BD+28 4211 has a faint red companion 2.8-arcsec away, and is only recommended for use in the blue channel in good seeing.

A model extinction curve for LBT

An extinction curve for the LBT site has yet to be measured and so, until this can be done, a model extinction curve for Mt. Graham has been constructed based on the KPNO and Paranal extinction curves scaled to an elevation of 3200-m assuming an atmospheric scale-height of 7000-m and combined.
The model LBT extinction curve contains two columns: wavelength [Angstroms] and extinction  [mag/airmass].

Table 2: LBT Model Extinction Curve

 

 λ (Å)  Kλ [mag/airmass]
 3200  0.866
 3500  0.511
 4000  0.311
 4500  0.207
 5000  0.153
 5500  0.128
 6000  0.113
 6450  0.088
 6500  0.085
 7000  0.063
 7500  0.053
 8000  0.044
 8210  0.043
 8260  0.042
 8370  0.041
 8708  0.026
 10256  0.020
The scaling ignores elevation-independent components of extinction like high-altitude (>5-10km) suspended aerosols, but that is a minority component and highly variable in any event (e.g., injection of particulates from volcanic eruptions, powerful sand storms, etc.). The table above also does not include time- and position-variable molecular absorption features of water-vapor, O2, and ozone.