A white dwarf accreting planetary material determined from X-ray observations

Area of Science:

• Astronomy and Astrophysics
• Stellar Evolution
• Exoplanetary Science

Background:

• Many white dwarf stars exhibit atmospheric pollution by heavy elements, suggesting accretion of planetary debris.
• Previous evidence relied on indirect photospheric metal detection, heavily dependent on atmospheric modeling.
• Direct measurement of accretion rates and compositions has been challenging.

Purpose of the Study:

• To directly measure the instantaneous accretion rate of a polluted white dwarf, G29-38.
• To test the hypothesis of ongoing debris accretion by analyzing X-ray emissions.
• To constrain accretion rates independently of stellar atmosphere models.

Main Methods:

• Detected X-ray emissions from the white dwarf G29-38 with a 4.4σ significance.
• Calculated the instantaneous accretion rate using the measured X-ray luminosity.
• Measured the plasma temperature of the accreting material.

Main Results:

• A direct, model-independent instantaneous accretion rate was derived from X-ray luminosity.
• The derived accretion rate for G29-38 is higher than previously estimated from photospheric abundances.
• A low plasma temperature (0.5 ± 0.2 keV) was measured, consistent with low-rate accretion models.

Conclusions:

• X-ray detection provides direct evidence of ongoing debris accretion onto white dwarfs.
• The higher accretion rate suggests potential limitations in current atmospheric models, possibly requiring convective overshoot.
• The findings support bombardment solutions for white dwarfs accreting at low rates.