Rotational velocities of the giants in symbiotic stars: III. Evidence of fast rotation in S-type symbiotics

TL;DR

This study measures the rotational velocities of giants in symbiotic stars, revealing they rotate significantly faster than similar field giants, which impacts their mass loss and ejection behaviors.

Contribution

It provides the first comprehensive comparison showing symbiotic giants rotate faster than field giants, with implications for their mass loss and ejection mechanisms.

Findings

K giants in S-type symbiotics rotate >4.5 km/s, 2-4 times faster than field K giants.

M giants in S-type symbiotics rotate 1.5 times faster than field M giants.

D'-type symbiotics are confirmed as fast rotators.

Abstract

We have measured the projected rotational velocities (vsini) in a number of symbiotic stars and M giants using high resolution spectroscopic observations. On the basis of our measurements and data from the literature, we compare the rotation of mass-donors in symbiotics with vsini of field giants and find that: (1) the K giants in S-type symbiotics rotate at vsini>4.5 km/s, which is 2-4 times faster than the field K giants; (2) the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. Statistical tests show that these differences are highly significant: p-value < 0.001 in the spectral type bins K2III-K5III, M0III-M6III, and M2III-M5III; (3) our new observations of D'-type symbiotics also confirm that they are fast rotators. As a result of the rapid rotation, the cool giants in symbiotics should have 3-30 times larger mass loss rates. Our results suggest also that bipolar ejections in symbiotics seem to happen in objects where the mass donors rotate faster than the orbital period. All spectra used in our series of papers can be obtained upon request from the authors.