Management for Users in ROCS

Exposure time calculator

The current exposure time calculator has been implemented using the zeropoints shown in the MEIA2 and ARES web pages. Similar values should be applicable to LAIA. The zeropoints provide an estimate of the limiting magnitude for an exposure time of 5 minutes (the maximum recommended) and S/N=100. They are based on observations in dark-clear nights with medium seeing for objects at zenith. Therefore, the results presented below do not consider sky brightness (around V~22 mag per arcsec) and should be considered orientative at best.

In order to determine the maximum exposure time before saturation with LAIA, values with a S/N=750 should ensure an optimum S/N within linearity regime of the CCD, except in cases with very good seeing or bright sky conditions.

Instrument 
Value to compute 
Filter 
Apparent magnitude 
Exposure time (sec) 
S/N ratio 
VPH 
Magnitude of the star 
Exposure time (sec) 

Exposure time calculator API

How It Works

The Exposure Time Calculator takes as inputs the target's magnitude, the filter in use, the desired Signal-to-Noise Ratio (SNR), and optionally, the airmass. It then returns the exposure time required to achieve the desired SNR in the chosen filter, accounting for atmospheric extinction at various wavelengths and airmass.

Input Format

To use the Exposure Time Calculator, format your input data in JSON as demonstrated below:

	  
  data = {
	'mag': TARGET_MAGNITUDE,   # Magnitude of the target
	'filter': FILTER_NAME,     # Same as in instrument_configuration
	'sn': SNR,                 # Desired SNR
	'airmass': OPTIONAL_AIRMASS # Optional (Default: 1.0)
  }

Example Usage

In order to use the Exposure Time Calculator API, the user needs to use a programming language capable of making HTTP requests to APIs, using the appropriate library or module. In the example below, we show how to request the exposure time for a given magnitude, filter, and SNR using Python:

	  
  import requests
  
  URL = "https://mur.ieec.cat/api/v1"
  
  # GENERATE INPUT DATA FOR THE EXPOSURE TIME CALCULATOR
  data = {'mag': 15.4, 'filter': 'R', 'sn': 50}  
  # SEND THE INPUT TO THE EXPOSURE TIME CALCULATOR API
  result = requests.get(f"{URL}/utils/exposure-time",
			params = data, verify = False)              
  exp_time = result.json()['exposure_time']
  
  print(f"Exposure time = {exp_time}s")

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