# The Herschel Orion Protostar Survey: Luminosity and Envelope Evolution

## TL;DR

This study uses Herschel data to analyze the luminosity and envelope evolution of over 300 protostars in Orion, revealing trends in brightness, envelope mass, and evolutionary stages with detailed SED modeling.

## Contribution

It provides a comprehensive analysis of protostellar luminosities and envelope masses, incorporating inclination and reddening corrections, and offers new insights into protostar evolution in Orion.

## Key findings

- Median luminosity decreases with bolometric temperature.
- Class 0 protostars are systematically brighter than Class I.
- Luminosity scatter at fixed envelope mass spans three orders of magnitude.

## Abstract

The Herschel Orion Protostar Survey obtained well-sampled 1.2 - 870 micron spectral energy distributions (SEDs) of over 300 protostars in the Orion molecular clouds, home to most of the young stellar objects (YSOs) in the nearest 500 pc. We plot the bolometric luminosities and temperatures for 330 Orion YSOs, 315 of which have bolometric temperatures characteristic of protostars. The histogram of bolometric temperature is roughly flat; 29% of the protostars are in Class 0. The median luminosity decreases by a factor of four with increasing bolometric temperature; consequently, the Class 0 protostars are systematically brighter than the Class I protostars, with a median luminosity of 2.3 L_sun as opposed to 0.87 L_sun. At a given bolometric temperature, the scatter in luminosities is three orders of magnitude. Using fits to the SEDs, we analyze how the luminosities corrected for inclination and foreground reddening relate to the mass in the inner 2500 AU of the best-fit model envelopes. The histogram of envelope mass is roughly flat, while the median corrected luminosity peaks at 15 L_sun for young envelopes and falls to 1.7 L_sun for late-stage protostars with remnant envelopes. The spread in luminosity at each envelope mass is three orders of magnitude. Envelope masses that decline exponentially with time explain the flat mass histogram and the decrease in luminosity, while the formation of a range of stellar masses explains the dispersion in luminosity.