apogee_etc

A starter hybrid exposure time calculator for APOGEE-like observations.

The design is intentionally split into:

1. A reusable Python package with the ETC engine.
2. Observatory/instrument configs for APO and LCO.
3. Empirical coefficients that can be calibrated from real APOGEE data.
4. A Streamlit app as a lightweight online interface.

Most numerical values are placeholders and should be replaced with values calibrated from real APOGEE exposures.

Install for development

cd apogee_etc
python -m pip install -e ".[app,test]"

Run the example

python examples/basic_usage.py

Run the web app

streamlit run app/streamlit_app.py

Run tests

pytest

Basic Python usage

from apogee_etc import calculate_snr, ETCInput

inp = ETCInput(
    observatory="APO",
    hmag=15.0,
    exptime_s=500,
    nexp=8,
    seeing_fwhm_arcsec=1.3,
    airmass=1.2,
)

out = calculate_snr(inp)
print(out.snr)

Calibration philosophy

The calculator combines a physically motivated noise equation with empirical coefficients:

• stellar count-rate zeropoint
• seeing dependence
• airmass dependence
• sky/background rate
• empirical noise floor

The placeholders are meant to be replaced by APO/LCO-specific fits to real exposures.