High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A*

Nishiyama, Shogo; Sato, Wakana; Hotta, Moeka; Ikarashi, Momoka; Saida, Hiromi; Takamori, Yohsuke; Nagata, Tetsuya; Ikeda, Hiroyuki; Takahashi, Masaaki

doi:10.3390/universe11100332

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High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A^*

by

Shogo Nishiyama

^1,*

,

Wakana Sato

¹,

Moeka Hotta

¹,

Momoka Ikarashi

¹,

Hiromi Saida

²

,

Yohsuke Takamori

³

,

Tetsuya Nagata

⁴

,

Hiroyuki Ikeda

⁵

and

Masaaki Takahashi

⁶

¹

Faculty of Education, Miyagi University of Education, Sendai 980-0845, Miyagi, Japan

²

Faculty of Liberal Arts, Daido University, Nagoya 457-8530, Aichi, Japan

³

National Institute of Technology (KOSEN), Wakayama College, Gobo 644-0023, Wakayama, Japan

⁴

Department of Astronomy, Kyoto University, Kyoto 606-8502, Japan

⁵

Organization for Fundamental Education, Fukui University of Technology, 3-6-1, Gakuen, Fukui 910-8505, Fukui, Japan

⁶

Department of Physics and Astronomy, Aichi University of Education, Kariya 448-8542, Aichi, Japan

^*

Author to whom correspondence should be addressed.

Universe 2025, 11(10), 332; https://doi.org/10.3390/universe11100332

Submission received: 25 August 2025 / Revised: 26 September 2025 / Accepted: 28 September 2025 / Published: 5 October 2025

(This article belongs to the Special Issue 10th Anniversary of Universe: Galaxies and Their Black Holes)

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Abstract

IRS 16CC and IRS 33N are among more than 100 young, massive stars identified within 0.5 pc from the Galactic central supermassive black hole Sgr A*, where conventional star formation processes are expected to be strongly suppressed. A subset of these stars, including IRS 16CC, has been confirmed to reside in a clockwise rotating stellar disk, and is thought to have formed in a massive, gaseous disk around Sgr A*. In contrast, other young massive stars, such as IRS 33N, exhibit dynamical behaviors that deviate significantly from those of the disk population, and their formation mechanism is still uncertain. To investigate their formation mechanism, we carried out near-infrared, high-resolution spectroscopic observations of IRS 16CC and IRS 33N using the Infrared Camera and Spectrograph on the Subaru telescope, equipped with an adaptive optics system. We compared the profiles of He I absorption lines with synthetic spectra generated from model atmospheres, and then compared derived stellar parameters with stellar evolutionary tracks to estimate their ages and initial masses. Our analysis yields their effective temperatures of ∼23,000 K, surface gravities of ∼2.8, and initial masses of

37 \pm 6 M_{⊙}

and

27_{- 3}^{+ 4} M_{⊙}

, consistent with spectral types of B0.5–1.5 supergiants. The ages of IRS 16CC and IRS 33N are estimated to be

4.4 \pm 0.7

Myr and

5 . 3_{- 0.7}^{+ 1.1}

Myr, respectively. These results suggest that, despite their different dynamical properties, the two stars are likely to share a common origin.

Keywords: star formation; Galactic center; massive stars

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MDPI and ACS Style

Nishiyama, S.; Sato, W.; Hotta, M.; Ikarashi, M.; Saida, H.; Takamori, Y.; Nagata, T.; Ikeda, H.; Takahashi, M. High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A^*. Universe 2025, 11, 332. https://doi.org/10.3390/universe11100332

AMA Style

Nishiyama S, Sato W, Hotta M, Ikarashi M, Saida H, Takamori Y, Nagata T, Ikeda H, Takahashi M. High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A^*. Universe. 2025; 11(10):332. https://doi.org/10.3390/universe11100332

Chicago/Turabian Style

Nishiyama, Shogo, Wakana Sato, Moeka Hotta, Momoka Ikarashi, Hiromi Saida, Yohsuke Takamori, Tetsuya Nagata, Hiroyuki Ikeda, and Masaaki Takahashi. 2025. "High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A^*" Universe 11, no. 10: 332. https://doi.org/10.3390/universe11100332

APA Style

Nishiyama, S., Sato, W., Hotta, M., Ikarashi, M., Saida, H., Takamori, Y., Nagata, T., Ikeda, H., & Takahashi, M. (2025). High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A^*. Universe, 11(10), 332. https://doi.org/10.3390/universe11100332

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High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation near Sgr A^*

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