Massive multiple star system found by astronomers

Representative examples of the spectrum of HD 64315 at
four different phases. Spectra are numbered for ease of
identification. Credit: Lorenzo et al., 2017.

A group of astronomers led by Javier Lorenzo of the
University of Alicante, Spain, has discovered that the binary
star system HD 64315 is more complex than previously thought.
The new study reveals that HD 64315 contains at least two
binary systems composed of massive stars. The findings
appeared online on Aug. 2 in a paper published on arXiv.org.

HD 64315 (also known as HIP 38430) is the main ionising source
of the Galactic H ii region Sh2-311. It was initially
classified by previous studies as a , located some 16,000 light years away
from the Earth. However, a new study conducted by Lorenzo’s
team reveals breakthrough information about this stellar
system.

The researchers have analyzed over 50 high-resolution spectra
of HD 64315 obtained during previous observations and also
photometric data from All Sky Automated Survey and Hipparcos
catalogs. This analysis revealed strong signatures of more than
two components present in the spectra, indicating that HD 64315
is, in fact, a multiple system comprising at least four
components.

“By using a complex procedure to analyse 52 high-resolution
spectra, we are able to confirm that HD 64315 contains two
binary systems, one of which is an eclipsing binary,” the paper
reads.

According to the research, HD 64315 is composed of at least two
, one of which is an
eclipsing binary. The two binaries are located about 500 AU
from each other.

HD 64315 AaAb is the non-eclipsing binary with an of 2.7 days. Both components of
this binary have minimal masses of at least 10 , but most likely about 30 solar
masses.

The eclipsing binary was designated HD 64315 BaBb and has a
much shorter orbital period which equals approximately one day.
Both stars of this binary have a similar mass of about 14.6
solar masses.

The researchers found that HD 64315 AaAb’s components are
hotter than those of the eclipsing binary, and dominate the
appearance of the whole system. They estimate that HD 64315 has
a total mass of above 90 solar masses. Notably, the eclipsing
binary is one the most massive overcontact binaries known, a
likely merger progenitor in a very wide multiple system.

The team does not exclude the possibility that HD 64315 could
be a compact cluster in which most of the mass could be
concentrated in the two observed binaries. “Lower-mass
components would not be observable in the glare of this very
bright system. However, in any case, it is highly unlikely that
HD 64315 is surrounded by a cluster with about 1,000 solar
masses, as is usual for other O6 V stars,” the authors noted.

In concluding remarks, the researchers emphasized that HD 64315
is potentially a massive hierarchical system that formed in a
sparse environment, which highlights the need for detailed
studies of multiplicity in apparently “isolated” .

“HD 64315 provides a cautionary tale about high-mass star
isolation and multiplicity. Its total mass is likely above 90
solar masses, but it seems to have formed without an
accompanying cluster,” the scientists concluded.

Explore further:

Another bee in the beehive—Astronomers discover binary star in
the NGC 2632 cluster

More information: arxiv.org/pdf/1708.00849.pdf

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