Category: Papers

Investigating episodic mass loss in evolved massive stars. I. Spectroscopy of dusty massive stars in ten southern galaxies

Bonanos, A. Z.; Tramper, F.; de Wit, S.; Christodoulou, E.; Muñoz Sanchez, G.; Antoniadis, K.; Athanasiou, S.; Maravelias, G.; Yang, M.; Zapartas, E.

Astronomy & Astrophysics, 686, 77 (2024)

ADS – Journal – arXiv

Abstract

Context. Episodic mass-loss events such as giant eruptions in luminous blue variables or pre-supernova eruptions in red supergiants drastically alter the evolutionary path of a massive star, resulting in a rich and complex circumstellar environment and IR excess. However, the incidence of these events, and hence their importance in massive star evolution, remains unknown.
Aims: The ASSESS project (Episodic Mass Loss in Evolved Massive Stars: Key to Understanding the Explosive early Universe) aims to determine the role of episodic mass loss in the evolution of massive stars. As a first step, we constructed a catalog of spectroscopically identified dusty, evolved massive stars in ten southern galaxies for which Spitzer point-source catalogs are available. The resulting catalog may be used to identify stars that have undergone an episodic mass-loss event. The target galaxies span a range of metallicities, Z = 0.06-1.6 Z⊙, allowing for the investigation of a potential metallicity dependence.
Methods: We conducted multi-object spectroscopy of dusty massive star candidates in ten target galaxies using the Very Large Telescope. We obtained 763 spectra from WLM, NGC 55, NGC 247, NGC 253, NGC 300, NGC 1313, NGC 3109, Sextans A, M83, and NGC 7793. The targets were selected using their Spitzer photometry, by prioritizing targets with a strong IR excess, which indicates the presence of hot dust. We determined a spectral classification for each target. Additionally, we used archival images from the Hubble Space Telescope (HST), available for 150 of our targets, to provide a visual classification for 80 targets, as a star, cluster, or galaxy.
Results: We provide a catalog of 541 spectroscopically classified sources that includes 185 massive stars, of which 154 are newly classified massive stars. The catalog contains 129 red supergiants, 27 blue supergiants, 10 yellow supergiants, 4 luminous blue variable candidates, 7 supergiant B[e] stars, and 8 emission-line objects. Evidence for circumstellar dust is found in 24% of these massive stars, based on their IR colors. We report a success rate of 28% for identifying massive stars from our observed spectra, while the average success rate of our priority system for selecting evolved massive stars is 36%. Additionally, the catalog contains 21 background galaxies (including active galactic nuclei and quasars), 10 carbon stars, and 99 H II regions. We measured the line ratios [N II]/Hα and [S II]/Hα for 76 H II regions and 36 other spectra with nebular emission lines, thereby identifying eight sources with shocked emission.
Conclusions: We present the largest catalog of evolved massive stars and in particular of red supergiants in nearby galaxies at low Z beyond the Local Group. The brightest and reddest of these are candidates for episodic mass loss. The fraction of dusty massive stars observed with respect to the initial selection is ~30%. We expect this catalog to trigger follow-up studies and pave the way for a comprehensive study of the eruptive late stages of massive star evolution in the era of the James Webb Space Telescope and the new survey telescopes (e.g., the Euclid mission, Nancy Grace Roman Space Telescope, and Vera C. Rubin Observatory).

Keywords: catalogs – circumstellar matter – stars: evolution – stars: massive – stars: mass-loss – supergiants

Evolved massive stars at low-metallicity. V. Mass-loss rate of red supergiant stars in the Small Magellanic Cloud

Yang, Ming; Bonanos, Alceste Z.; Jiang, Biwei ; Zapartas, Emmanouil; Gao, Jian ; Ren, Yi ; Lam, Man I. ; Wang, Tianding ; Maravelias, Grigoris; Gavras, Panagiotis ; Wang, Shu ; Chen, Xiaodian; Tramper, Frank; de Wit, Stephan; Chen, Bingqiu ; Wen, Jing ; Liu, Jiaming ; Tian, Hao ; Antoniadis, Konstantinos; Luo, Changqing

Astronomy & Astrophysics, 676, 84 (2023)

ADS – Journal – arXiv

Abstract

The mass-loss rate (MLR) is one of the most important parameters in astrophysics, because it impacts many areas of astronomy, such as ionizing radiation, wind feedback, star-formation rates, initial mass functions, stellar remnants, supernovae, and so on. However, the most important modes of mass loss are also the most uncertain, as the dominant physical mechanisms that lead to this phenomenon are stull largely unknown. Here we assemble the most complete and clean red supergiant (RSG) sample (2121 targets) so far in the Small Magellanic Cloud (SMC) with 53 different bands of data to study the MLR of RSGs. In order to match the observed spectral energy distributions (SEDs), we created a theoretical grid of 17 820 oxygen-rich models (“normal” and “dusty” grids are half-and-half) using the radiatively driven wind model of the DUSTY code, covering a wide range of dust parameters. We select the best model for each target by calculating the minimal modified chi-square and visual inspection. The resulting MLRs from DUSTY are converted to real MLRs based on the scaling relation, for which a total MLR of 6.16 × 10−3 M⊙ yr−1 is measured (corresponding to a dust-production rate of ∼6 × 10−6 M⊙ yr−1), with a typical MLR of ∼10−6 M⊙ yr−1 for the general population of the RSGs. The complexity of mass-loss estimations based on the SED is fully discussed for the first time, and our results indicate large uncertainties based on the photometric data (potentially up to one order of magnitude or more). The Hertzsprung-Russell (HR) and luminosity versus median-absolute-deviation (MAD) diagrams of the sample indicate the positive relation between luminosity and MLR. Meanwhile, the luminosity versus MLR diagrams show a “knee-like” shape with enhanced mass loss occurring above log10(L/L⊙)≈4.6, which may be due to the degeneracy of luminosity, pulsation, low surface gravity, convection, and other factors. We derive our MLR relation using a third-order polynomial to fit the sample and compare our results with previous empirical MLR prescriptions. Given that our MLR prescription is based on a much larger sample than previous determinations, it provides a more accurate relation at the cool and luminous region of the HR diagram at low metallicity compared to previous studies. Finally, nine targets in our sample were detected in the UV, which could be an indicator of OB-type companions of binary RSGs.

Keywords: infrared: stars; galaxies: dwarf; stars: late-type; stars: massive; stars: mass-loss; Astrophysics – Solar and Stellar Astrophysics

X-Shooting ULLYSES: Massive stars at low metallicity. I. Project description

Vink, Jorick S. ; Mehner, A. ; Crowther, P. A. ; Fullerton, A. ; Garcia, M. ; Martins, F. ; Morrell, N. ; Oskinova, L. M. ; St-Louis, N. ; ud-Doula, A. ; Sander, A. A. C. ; Sana, H. ; Bouret, J. -C. ; Kubátová, B. ; Marchant, P. ; Martins, L. P. ; Wofford, A. ; van Loon, J. Th. ; Grace Telford, O. ; Götberg, Y. ; Bowman, D. M.; Erba, C. ; Kalari, V. M. ; Abdul-Masih, M. ; Alkousa, T. ; Backs, F. ; Barbosa, C. L. ; Berlanas, S. R. ; Bernini-Peron, M. ; Bestenlehner, J. M. ; Blomme, R. ; Bodensteiner, J. ; Brands, S. A. ; Evans, C. J. ; David-Uraz, A. ; Driessen, F. A. ; Dsilva, K. ; Geen, S. ; Gómez-González, V. M. A. ; Grassitelli, L. ; Hamann, W. -R. ; Hawcroft, C. ; Herrero, A. ; Higgins, E. R. ; John Hillier, D. ; Ignace, R. ; Istrate, A. G. ; Kaper, L. ; Kee, N. D. ; Kehrig, C. ; Keszthelyi, Z. ; Klencki, J. ; de Koter, A. ; Kuiper, R. ; Laplace, E. ; Larkin, C. J. K. ; Lefever, R. R. ; Leitherer, C. ; Lennon, D. J. ; Mahy, L. ; Maíz Apellániz, J. ; Maravelias, G. ; Marcolino, W. ; McLeod, A. F. ; de Mink, S. E. ; Najarro, F. ; Oey, M. S. ; Parsons, T. N. ; Pauli, D. ; Pedersen, M. G. ; Prinja, R. K. ; Ramachandran, V. ; Ramírez-Tannus, M. C. ; Sabhahit, G. N. ; Schootemeijer, A. ; Reyero Serantes, S. ; Shenar, T. ; Stringfellow, G. S. ; Sudnik, N. ; Tramper, F. ; Wang, L.

Astronomy & Astrophysics, 675, 154 (2023)

ADS – Journal – arXiv

Abstract

Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational wave events involving spectacular black hole mergers indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observing ∼250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES programme. The complementary X-Shooting ULLYSES (XShootU) project provides an enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESO’s Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates as a function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of astrophysics, the data and modelling of the XShootU project is expected to be a game changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope spectra of the first stellar generations, the individual spectra of low-Z stars need to be understood, which is exactly where XShootU can deliver.

Keywords: stars: atmospheres; stars: early-type; stars: winds; outflows; stars: evolution; methods: observational; galaxies: dwarf; Astrophysics – Solar and Stellar Astrophysics; Astrophysics – Cosmology and Nongalactic Astrophysics; Astrophysics – Astrophysics of Galaxies; Astrophysics – High Energy Astrophysical Phenomena

Discovering New B[e] Supergiants and Candidate Luminous Blue Variables in Nearby Galaxies

Maravelias, Grigoris; de Wit, Stephan; Bonanos, Alceste Z.; Tramper, Frank; Munoz-Sanchez, Gonzalo; Christodoulou, Evangelia

Galaxies, 11, 79 (2023)

ADS – Journal – arXiv

Abstract

Mass loss is one of the key parameters that determine stellar evolution. Despite the progress we have achieved over the last decades we still cannot match the observational derived values with theoretical predictions. Even worse, there are certain phases, such as the B[e] supergiants (B[e]SGs) and the Luminous Blue Variables (LBVs), where significant mass is lost through episodic or outburst activity. This leads to various structures forming around them that permit dust formation, making these objects bright IR sources. The ASSESS project aims to determine the role of episodic mass in the evolution of massive stars, by examining large numbers of cool and hot objects (such as B[e]SGs/LBVs). For this purpose, we initiated a large observation campaign to obtain spectroscopic data for ∼1000 IR-selected sources in 27 nearby galaxies. Within this project we successfully identified seven B[e] supergiants (one candidate) and four Luminous Blue Variables of which six and two, respectively, are new discoveries. We used spectroscopic, photometric, and light curve information to better constrain the nature of the reported objects. We particularly noted the presence of B[e]SGs at metallicity environments as low as 0.14 Z⊙.

Keywords: Astrophysics – Astrophysics of Galaxies; Astrophysics – Solar and Stellar Astrophysics

Properties of luminous red supergiant stars in the Magellanic Clouds

de Wit, S.; Bonanos, A. Z.; Tramper, F. ; Yang, M.; Maravelias, G. ; Boutsia, K. ; Britavskiy, N. ; Zapartas, E.

Astronomy & Astrophysics, 669, 86 (2023)

ADS – Journal – arXiv

Abstract

Context. There is evidence that some red supergiants (RSGs) experience short-lived phases of extreme mass loss, producing copious amounts of dust. These episodic outburst phases help strip the hydrogen envelope from evolved massive stars, drastically affecting their evolution. However, to date, the observational data of episodic mass loss is limited.
Aims: This paper aims to derive surface properties of a spectroscopic sample of 14 dusty sources in the Magellanic Clouds using the Baade telescope. These properties can be used for future spectral energy distribution fitting studies to measure the mass-loss rates from present circumstellar dust expelled from the star through outbursts.
Methods: We applied MARCS models to obtain the effective temperature (Teff) and extinction (AV) from the optical TiO bands. We used a χ2 routine to determine the model that best fits the obtained spectra. We computed the Teff using empirical photometric relations and compared this to our modelled Teff.
Results: We have identified a new yellow supergiant and spectroscopically confirmed eight new RSGs and one bright giant in the Magellanic Clouds. Additionally, we observed a supergiant B[e] star and find that the spectral type has changed compared to previous classifications, confirming that the spectral type is variable over decades. For the RSGs, we obtained the surface and global properties, as well as the extinction (AV).
Conclusions: Our method has picked up eight new, luminous RSGs. Despite selecting dusty RSGs, we find values for AV that are not as high as expected given the circumstellar extinction of these evolved stars. The most remarkable object from the sample, LMC3, is an extremely massive and luminous evolved massive star and may be grouped amongst the largest and most luminous RSGs known in the Large Magellanic Cloud (log(L*/L⊙) ~ 5.5 and R = 1400 R⊙).

Keywords: stars: massive; supergiants; stars: fundamental parameters; stars: atmospheres; stars: late-type; Magellanic Clouds; Astrophysics – Solar and Stellar Astrophysics; Astrophysics – Astrophysics of Galaxies