ETC module

Introduction

etc is a module with tools for exposure time calculation.

It allows a user to set up Object, Atmosphere, Telescope, Instrument, and Observation objects, and then use the latter to calculate the flux from an object, an exposure time given a desired S/N, or S/N given an exposure time.

etc works in both a spectral mode, giving S/N per pixel (given a dispersion), and also an imaging mode, in which the spectrum is integrated over.

Usage

The user instatiates Object, Atmosphere, Telescope, and Instrument objects.

The Object object specifies a magnitude and SED.

The Atmosphere object specifies a moon phase. Emission spectra are taken from the ESO sky calculator for moon phase (to the closest 0.1).

The Telescope object takes a telescope name or a diameter.

The Instrument object takes an instrument name or a single, wavelength-independent throughput.

These are then passed when an Observation object is instatiated.

Module functions

class pyvista.etc.Atmosphere(name='', transmission=0.8)

class representing the Earth’s atmosphere

emission(wave, moonphase)

Returns atmospheric emission (photon flux) at input wavelengths

throughput(wave)

Returns atmospheric transmission at input wavelengths

class pyvista.etc.Detector(name='', efficiency=0.8, rn=5)

class representing a detector

throughput(wave)

Returns detector efficiency at input wavelengths

class pyvista.etc.Instrument(name='', efficiency=0.8, pixscale=1, dispersion=<Quantity 1. Angstrom>, rn=0)

class representing an Instrument

filter(wave, filter='', cent=<Quantity 5500. Angstrom>, wid=<Quantity 850. Angstrom>, trans=0.8)

Returns filter throughput at input wavelengths

throughput(wave)

Returns instrument throughput at input wavelengths

class pyvista.etc.Mirror(type, const=0.9)

class representing a mirror given coating name, provide method for reflectivity

reflectivity(wave)

Returns reflectivity at input wavelengths

class pyvista.etc.Object(type='bb', teff=10000, mag=0, refmag='V')

Class representing an object Given a type (blackbody or input spectrum) and a magnitude, provides method for Fnu, Flam, photon flux

flam(wave)

Return SED in Flambda

fnu(wave)

Return SED in Fnu

photflux(wave)

Return SED in photon flux

sed(wave)

Return sed in Fnu or Flambda, with units (depending on source of data)

class pyvista.etc.Observation(obj=None, atmos=None, telescope=None, instrument=None, wave=<Quantity [3000., 3001., 3002., ..., 9997., 9998., 9999.] Angstrom>, seeing=1, phase=0.0)

Object representing an observation

back_counts()

Return integrated photon flux for background

back_photonflux()

Return photon flux for background

counts()

Return integrated photon flux

exptime(sn)

Calculate exptime given S/N

photonflux()

Return photon flux

sn(t)

Calculate S/N given exposure time

class pyvista.etc.Telescope(name='', diameter=<Quantity 1. m>, mirrors=['Al'])

Class representing a telescope Given a name (or diameter and mirror array), provide methods area throughput

area()

Return telescope collecting area

throughput(wave)

Return telescope throughput at input wavelengths

pyvista.etc.signal(wave=<Quantity [4000., 5000., 6000., 7000.] Angstrom>, teff=7000, mag=10, telescope='ARC3.5M', it=0.8, at=0.8, phase=0.0, sn=100, ft=0.8, rn=0, plot=True)

Sets up input objects and observation for a S/N calculation