Dear Colleagues,

Star formation is one of the key questions of modern astronomy. Throughout the history of the Milky Way, the process of formation of new stars is not interrupted. Our observations demonstrate that stars are formed in small or larger groups called star clusters or associations.

Photometric and spectral variability is a fundamental characteristic of young stellar objects. Photometric variability is manifested as transient increases in brightness (outbursts), temporary drops in brightness (eclipses), and irregular or regular variations for short or long time scales. It targets active star-forming regions with the aim of discovering and quantifying their variability in terms of amplitude, timescale, and recurrence.

The spectroscopic variability is another basic characteristic of the young stars. Line profile variability is a common property which is especially true for the Hα emission line—the most prominent feature in the spectra of young stars. Studies of the photometric and spectroscopic variability of young stellar objects are very important to improving our understanding of the early stages of stellar evolution. This Special Issue of Symmetry is dedicated to the results of research in the fields of star formation.

Prof. Dr. Evgeni Semkov
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• star formation
• pre-main sequence stars
• protostars
• variables: T Tauri, Herbig Ae/Be stars
• open clusters and associations
• Herbig–Haro objects
• jets and outflows