Observations reveal complex environment of HD 50138

May 14, 2018 by Tomasz Nowakowski, Phys.org report
Spectra, visibilities, differential phases and closure phase for each baseline observation, of the Brγ line (left) and high-n Pfund lines (right) for HD 50138. The dashed lines correspond to the systemic velocities of the lines. Flux is normalized to the continuum. Credit: Koutoulaki et al., 2018.

Using European Southern Observatory's Very Large Telescope (VLT) European astronomers have uncovered a complex circumstellar environment of the star HD 50138. The finding, which could provide important clues about the evolutionary status of this star, was presented in a paper published May 3 on the arXiv pre-print repository.

Located some 1,100 light years away from the Earth, HD 50138 is a Herbig Be star of spectral type B8, about seven times larger and six times more massive than our sun. With a lumonisity of approximately 1,000 solar luminosities, it is one of the brightest Be in the southern sky.

The evolutionary status of HD 50138 is still unclear. Some astronomers suggests that it as a pre-main sequence star, while others propose that it should be considered as an evolved object close to turn-off from the main sequence. Moreover, it is also not clear whether HD 50138 is part of the Orion Monoceros molecular cloud complex or not associated with any star-forming region. Determining such a possible association could provide additional hints of the age of this star.

In order to learn more insights into the nature of HD 50138, a team of researchers led by Maria Koutoulaki of the Dublin Institute for Advanced Studies in Dublin, Ireland, conducted near-infrared interferometric observations of the innermost circumstellar environment of this star. For this purpose they employed the VLT-Interferometer (VLTI) with the beam combiner AMBER (Astronomical Multi-BEam combineR). This instrument allowed the scientists to find that the star's circumstellar environment is very complex.

"We report observations of the Herbig B[e] star, HD 50138, using VLTI/AMBER interferometric observations in the K band at medium spectral resolution. (…) Our results reveal that the circumstellar environment is very complex," the researchers wrote in the paper.

Study unveils that the spectrum of HD 50138 shows continuum emission, as well as hydrogen emission lines of bright Brackett-gamma and faint high-n Pfund. The researchers underlined that this in contrast to previous studies that detected only continuum and Brackett-gamma line emission.

"Our observations allowed us to map the size of the continuum emission and of the Brγ and high-n Pfund lines. The latter is detected for the first time," the paper reads.

The researchers estimated that the region of continuum emission has a projected size between 0.6 and 1.0 AU. When it comes to hydrogen lines, the projected size is about 0.4 AU. Moreover, they noted that both continuum and Brackett-gamma lines were found to trace an asymmetric origin but with opposing directions of asymmetries.

In concluding remarks, the astronomers wrote that results regarding and hydrogen lines, including morphology of the regions indicate complex circumstellar environment of HD 50138. They added that their findings also suggest that the studied object is most likely an evolved star.

"Finally, although we cannot exclude the possibility that HD 50138 is a young star our results point to an evolved source," the researchers concluded.

Explore further: Researchers study complex morphology of the protoplanetary disc around star MWC 758

More information: The circumstellar environment of HD50138 revealed by VLTI/AMBER at high angular resolution, arXiv:1805.01432 [astro-ph.SR] arxiv.org/abs/1805.01432

Abstract
HD50138 is a Herbig B[e] star with a circumstellar disc detected at IR and mm wavelength. Its brightness makes it a good candidate for NIR interferometry observations. We aim to resolve, spatially and spectrally, the continuum and hydrogen emission lines in the 2.12-2.47 micron region, to shed light on the immediate circumstellar environment of the star. VLTI/AMBER K-band observations provide spectra, visibilities, differential phases, and closure phases along three long baselines for the continuum, and HI emission in Brγ and five high-n Pfund lines. By computing the pure-line visibilities, we derive the angular size of the different line-emitting regions. A simple LTE model was created to constrain the physical conditions of HI emitting region. The continuum region cannot be reproduced by a geometrical 2D elongated Gaussian fitting model. We estimate the size of the region to be 1 au. We find the Brγ and Pfund lines come from a more compact region of size 0.4 au. The Brγ line exhibits an S-shaped differential phase, indicative of rotation. The continuum and Brγ line closure phase show offsets of ∼-25±5o and 20±10o, respectively. This is evidence of an asymmetry in their origin, but with opposing directions. We find that we cannot converge on constraints for the HI physical parameters without a more detailed model. Our analysis reveals that HD50138 hosts a complex circumstellar environment. Its continuum emission cannot be reproduced by a simple disc brightness distribution. Similarly, several components must be evoked to reproduce the interferometric observables within the Brγ, line. Combining the spectroscopic and interferometric data of the Brγ and Pfund lines favours an origin in a wind region with a large opening angle. Finally, our results point to an evolved source.

Related Stories

The mysterious star MWC349

December 1, 2017

Molecular clouds in interstellar space can sometimes produce natural masers (the radio wavelength analogs of lasers) that shine with bright, narrow beams of radiation. Regions of active star formation generate some of the ...

Astronomers take a closer look at a young circumbinary disk

April 10, 2017

(Phys.org)—In a research paper published Apr. 3 on arXiv.org, astronomers presented a close-up view of the circumbinary disk HD 142527 obtained with the Atacama Large Millimeter and submillimeter Array (ALMA) in Chile. ...

Magnetic fields discovered in two hot evolved stars

January 3, 2018

Astronomers have presented the initial results of the Large Impact of Magnetic Fields on the Evolution of Hot Stars (LIFE) project. Among determining fundamental parameters of 15 stars, they found that two of them have magnetic ...

Recommended for you

Long lost Galileo letter found at Royal Society library

September 26, 2018

Nature journalist Alison Abbott has published a News and Comment piece in the journal detailing the finding of a letter in a Royal Society library purported to have been written by famed early scientist Galileo Galilei. The ...

Software finds the best way to stick a Mars landing

September 26, 2018

Selecting a landing site for a rover headed to Mars is a lengthy process that normally involves large committees of scientists and engineers. These committees typically spend several years weighing a mission's science objectives ...

Hyper Suprime-Cam survey maps dark matter in the universe

September 26, 2018

Today, an international group of researchers, including Carnegie Mellon University's Rachel Mandelbaum, released the deepest wide field map of the three-dimensional distribution of matter in the universe ever made and increased ...

Tracking the interstellar object 'Oumuamua to its home

September 25, 2018

A team of astronomers led by Coryn Bailer-Jones of the Max Planck Institute for Astronomy has tracked the interstellar object 'Oumuamua to several possible home stars. The object was discovered in late 2017 – this was the ...

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.