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Find stellar activity timelines

Activity timelines (How-to)

Goal

Compute how long a star (or a cluster of stars) stays above an activity threshold (e.g., X-ray luminosity) or how long it remains in the saturated regime.

Prerequisites

Install MORS and download stellar evolution data:

pip install fwl-mors
mors download all

Units: thresholds must match the quantity you use (e.g., Lx in erg s⁻¹). Ages returned are in Myr.

Compute activity threshold

Option 1: Use the standalone helper on an explicit track (basic)

mors.ActivityLifetime takes an age array and a track array and returns the age when the track finally drops below the threshold.

import mors

AgeThreshold = mors.ActivityLifetime(
    Age=star.AgeTrack,
    Track=star.LxTrack,
    Threshold=1.0e28
)
print(AgeThreshold)

Behavior: - If the track crosses the threshold multiple times → returns the final crossing time. - If it never goes below the threshold → returns the final age in the track. - If it is never above the threshold → returns 0.0.

Optional: limit the search to ages below AgeMax.

This version selects the track internally; you only provide the quantity name and threshold.

AgeThreshold = star.ActivityLifetime(Quantity="Lx", Threshold=1.0e28)
print(AgeThreshold)

You can also set a maximum age to consider:

AgeThreshold = star.ActivityLifetime(Quantity="Lx", Threshold=1.0e28, AgeMax=1000.0)

Note: The Quantity string must match one of the supported activity tracks:

  • Lx, Fx, Rx, FxHZ
  • Leuv1, Feuv1, Reuv1, Feuv1HZ
  • Leuv2, Feuv2, Reuv2, Feuv2HZ
  • Leuv, Feuv, Reuv, FeuvHZ
  • Lly, Fly, Rly, FlyHZ

Compute cluster lifetimes (same interface, returns arrays)

For a mors.Cluster, the call is the same but returns one value per star:

AgeThreshold = cluster.ActivityLifetime(Quantity="Lx", Threshold=1.0e28)
print(AgeThreshold)  # numpy array

Compute saturation lifetime

To get the time the star remains in the saturated regime, pass Threshold="sat":

AgeSaturated = star.ActivityLifetime(Quantity="Lx", Threshold="sat")
print(AgeSaturated)

Note: the choice of Quantity should not change the saturation lifetime (XUV quantities saturate together), but it must be a valid option.

Common pitfalls

  • Make sure your Threshold uses the same units as the chosen Quantity (e.g., Lx is erg s⁻¹).
  • The function returns the final threshold crossing time if there are multiple crossings.