New study uncovers insights about the nature of the ultraviolet-bright star Barnard 29

March 11, 2019 by Tomasz Nowakowski, Phys.org report
New study uncovers insights about the nature of the ultraviolet-bright star Barnard 29
GHRS spectrum of Barnard 29. Credit: Dixon et al., 2019.

Analyzing data from spectroscopic instruments, astronomers have reported fundamental properties of Barnard 29, an ultraviolet-bright star in globular cluster Messier 13. Results of the analysis, presented in a paper published March 1 on arXiv.org, provide important insights into the nature of this star.

Barnard 29 has intrigued astronomers for over a century. It was described in the earliest studies as the most striking example of a star shining with a much bluer light than the great majority of the cluster's other . According to more recent observations, Barnard 29 is classified as an ultraviolet-bright, post- (AGB) star.

Although Barnard 29 has been a subject of numerous observations, still many questions about its evolution and remain unanswered. So a team of astronomers led by William V. Dixon of Space Telescope Science Institute in Baltimore, Maryland, has combed through the available data from the Hubble Space Telescope's FUSE, COS and GHRS spectroscopic instruments and from the HIRES echelle spectrograph on the Keck I telescope in Hawaii. Analysis of this dataset allowed the researchers to determine chemical abundances for more than dozen elements in this star.

"The availability of high-resolution, high signal-to-noise FUV and optical spectra allow us to confirm the star's iron abundance and determine the abundances of many additional species," the astronomers wrote in the paper.

The research revealed that Barnard 29 has chemical composition typical for first-generation stars in Messier 13. The object was found to be richer in oxygen and poorer in aluminum than second-generation stars in this cluster.

However, the star exhibits an underabundance of carbon and an overabundance of nitrogen, which indicates that it experienced a non-convective mixing on the red-giant branch (RGB) and did not undergo third dredge-up. Moreover, chemical abundances of Barnard 29 appear to have changed little since it left the RGB.

"The abundance pattern seen in Barnard 29—C depletion and N enhancement relative to the average value for first-generation stars on the RGB—suggests that the star experienced the full impact of deep mixing," the paper reads.

Furthermore, the researchers found that Barnard 29 has an effective temperature of approximately 21,400 K and a mass of about 0.5 solar masses. They also found that iron abundance of this star is -6.05, consistent with the mean value for Messier 13.

According to the paper, results of the study suggest that Barnard 29 evolved from a zero-age horizontal-branch (ZAHB) star with a mass of around 0.5-0.55 solar masses, near the boundary between the extreme and blue horizontal branches.

"In light of stellar-evolution models, it seems likely that Barnard 29 is a post-HB star evolving from a ZAHB star with MZAHB between 0.50 and 0.55 M, a range spanning the EHB/BHB boundary. A post-HB star would have fully ascended the RGB, consistent with our suggestion that Barnard 29 experienced the full effects of non-convective mixing on the RGB," the scientists explained.

Explore further: Astronomers reveal insights into the nature of a distant ultraviolet-bright star

More information: William V. Dixon et al. Observations of the Ultraviolet-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205). arXiv:1903.00350 [astro-ph.SR]. arxiv.org/abs/1903.00350

Related Stories

Multiple stellar populations detected in the cluster Hodge 6

February 18, 2019

Using ESO's Very Large Telescope (VLT), astronomers have found that the cluster Hodge 6 hosts multiple stellar populations. The detection could provide important hints on the formation and evolution of Hodge 6 and star clusters ...

Recommended for you

Physicists discover new class of pentaquarks

March 26, 2019

Tomasz Skwarnicki, professor of physics in the College of Arts and Sciences at Syracuse University, has uncovered new information about a class of particles called pentaquarks. His findings could lead to a new understanding ...

Study finds people who feed birds impact conservation

March 26, 2019

People in many parts of the world feed birds in their backyards, often due to a desire to help wildlife or to connect with nature. In the United States alone, over 57 million households in the feed backyard birds, spending ...

Matter waves and quantum splinters

March 25, 2019

Physicists in the United States, Austria and Brazil have shown that shaking ultracold Bose-Einstein condensates (BECs) can cause them to either divide into uniform segments or shatter into unpredictable splinters, depending ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.