The Luminous Blue Variable RMC 127 as Seen with ALMA and ATCA

C. Agliozzo (1,2), C. Trigilio (3), G. Pignata (2,1) , N. M. Phillips (4,5), R. Nikutta (6,7), P. Leto (3), G. Umana (3), A. Ingallinera (3), C. Buemi (3), F. E. Bauer (1,7,8), R. Paladini (9), A. Noriega-Crespo (10), J. L. Prieto (1,11), M. Massardi (12), and L. Cerrigone (13)

1) Millennium Institute of Astrophysics (MAS), Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago, Chile;
2) Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, 8320000, Chile
3) INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123, Catania Italy
4) European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
5) Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
6) National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
7) Instituto de Astrofísica and Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
8) Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
9) Infrared Processing Analysis Center, California Institute of Technology, 770 South Wilson Avenue, Pasadena, CA 91125, USA
10) Space Telescope Science Institute, Space Telescope Science Institute 3700 San Martin Drive, Baltimore, MD 21218, USA
11) Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
12) INAF-Istituto di Radioastronomia, via Gobetti 101, I-40129, Bologna, Italy
13) ASTRON, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands

We present ALMA and ATCA observations of
the luminous blue variable \rmc. The radio maps show for the first
time the core of the nebula and evidence that the nebula is strongly
asymmetric with a Z-pattern shape. Hints of this morphology are also
visible in the archival \emph{HST} $\rm H\alpha$ image, which
overall resembles the radio emission. The emission mechanism in the
outer nebula is optically thin free-free in the radio. At
high frequencies, a component of point-source emission appears at
the position of the star, up to the ALMA frequencies. The rising
flux density distribution ($S_{\nu}\sim \nu^{0.78\pm0.05}$) of this
object suggests thermal emission from the ionized stellar wind and
indicates a departure from spherical symmetry with
$n_{e}(r)\propto r^{-2}$. We examine different scenarios to explain
this excess of thermal emission from the wind and show that this can
arise from a bipolar outflow, supporting the suggestion by other
authors that the stellar wind of \rmc is aspherical. We fit the data
with two collimated ionized wind models and we find that the
mass-loss rate can be a factor of two or more smaller than in the
spherical case. We also fit the photometry obtained by IR space
telescopes and deduce that the mid- to far-IR emission must arise
from extended, cool ($\sim80\,\rm K$) dust within the outer ionized
Finally we discuss two possible scenarios for the nebular morphology: the canonical single star expanding shell geometry, and a precessing jet model assuming presence of a companion star.

Reference: ApJ, published online
Status: Manuscript has been accepted