# Magnetic fields of peculiar HgMn A type stars

Do HgMn (peculiar A type) stars really possess global magnetic fields? See, for example, this paper by Hubrig et al. from 2012.

• 'Do they possess magnetic fields'... Not 'are they possess magnetic fields'. Why do you ask? Is there something about the paper that is a problem for you? Is there a reason why you would find it surprising to have it claimed that HgMn stars have a magnetic field, al beit a weak one? – Jeremy Mar 13 '14 at 10:39
• My interpretation of the question (and of course correct me if I'm wrong) was that @user2579566 was asking if the magnetic fields exist on these stars, due to the ongoing debate in the scientific community. Is that the case, or am I off-track? – HDE 226868 Aug 13 '14 at 17:42
• Yes, you are right @HDE226868 – user2579566 Aug 14 '14 at 10:35
• So, what does the paper say about? – Py-ser Nov 24 '14 at 1:54
• A related meta discussion. The issue here is that the answer to this is a "We're not sure", but I'm reluctant to post an answer built around that. – HDE 226868 Nov 30 '14 at 2:41

## 1 Answer

One thing that seems to be clear is that HgMn stars have only an extremely weak net longitudinal magnetic field component, if any. Shorlin et al. (2002) did an early survey of HgMn, Am, and Ap stars, and detected no longitudinal magnetic fields in the former, with a median 1$\sigma$ uncertainty of 39 Gauss. Makaganiuk et al. (2010) also found $B_z$ values of 0 in the stars they surveyed, with a higher precision - a 1$\sigma$ uncertainty of 0.81-10 Gauss, varying between stars. Other studies also yielded precisions of less than a few Gauss for some stars (see mentions by Makaguniak (2011)).

Some reports have found longitudinal values in the 10s to 100s of Gauss, but as Kochukhov notes, subsequent inveistigations have failed to confirm these findings, which have had extremely high uncertainties. One example is Hubrig et al. (2012), the paper you cite, which claimed to have found weak longitudinal and quadratic fields in several stars, including HD 65949. Kochukhov et al. (2013) then found no longitudinal fields on the star, to within a few Gauss, and Bagnulo et al. (2013) attributed to 2012 findings to instrument error, leading to flawed data.

Non-longitudinal magnetic fields have not been observed in much detail (small-scale longitudinal fields have not yet been ruled out, either, by large-scale global ones appear to be nonexistent), and complicated ones could still exist. Kochukhov et al. (2013) do say that they have ruled out large so-called tangled magnetic fields, but small-scaled ones are still possible, according to Hubrig.

One thing worth noting is that the vast majority of these studies, including the one you referenced, which has been disputed, are focused on B-type HgMn stars, in part because fewer A-type HgMn stars have been discovered.