[Paper Review] The Long Secondary Period (LSP) Variables: Overview and Some Analysis

John R. Percy, Mayank H. Shenoy|arXiv (Cornell University)|Dec 8, 2023

Stellar, planetary, and galactic studies4 citations

TL;DR

This paper investigates Long Secondary Period (LSP) variables—red giants with prominent secondary variability periods—using ASAS-SN and AAVSO data. It finds that LSP amplitude peaks in moderate-luminosity stars and is smallest in Mira variables, supporting the eclipsing dust-enshrouded companion model, with LSP and pulsation periods increasing with stellar size and luminosity.

ABSTRACT

We briefly review the phenomenon of long secondary periods (LSPs) in red giants, and the LSP variable stars classification introduced in the All-Sky Automated Survey for Supernovae (ASAS-SN) variable star catalog; they are red giant Long Period Variables (LPVs) in which their LSP variability is significantly greater than their pulsational variability. We then describe and discuss the results of a period and amplitude analysis of a random sample of 35 LSP variables in the ASAS-SN catalog, using ASAS-SN data and the AAVSO VStar time-series analysis software. The pulsation period and amplitude, and LSP, all increase with increasing luminosity or size of the star, as expected. The behavior of the LSP amplitude is more complicated; it appears to be larger in moderate-luminosity stars, and smaller in low- and high-luminosity stars. In particular, it is relatively small in a sample of 27 Mira stars, analyzed separately using AAVSO visual data. These results are discussed in the context of the current model for the LSP phenomenon, namely that it is caused by eclipses of the red giant star by a dust-enshrouded companion.

Motivation & Objective

• To characterize the period and amplitude behavior of Long Secondary Period (LSP) variables in red giants.
• To investigate the relationship between LSP variability and stellar luminosity or size.
• To examine the amplitude of LSP variability across different luminosity regimes, particularly in Mira stars.
• To test the eclipsing dust-enshrouded companion model for LSP phenomena using observational data.
• To provide a statistical analysis of LSP behavior in a random sample of 35 LSP variables from the ASAS-SN catalog.

Proposed method

• Selected a random sample of 35 LSP variables from the ASAS-SN variable star catalog.
• Performed period and amplitude analysis using ASAS-SN light curves and the AAVSO VStar time-series analysis software.
• Analyzed pulsation period and amplitude, and LSP amplitude, as functions of stellar luminosity and size.
• Conducted a separate analysis of 27 Mira stars using AAVSO visual magnitude data.
• Correlated observed LSP amplitudes with stellar evolutionary state and luminosity to test the eclipsing companion hypothesis.
• Used statistical trends in period and amplitude to infer physical mechanisms behind LSP variability.

Experimental results

Research questions

• RQ1 How do the LSP period and amplitude vary with increasing luminosity or size of red giant stars?
• RQ2 Why is the LSP amplitude smaller in Mira stars compared to other LSP variables?
• RQ3 What is the relationship between pulsation period and LSP period in LSP variables?
• RQ4 Do the observed trends in LSP amplitude support the eclipsing dust-enshrouded companion model?
• RQ5 How does the amplitude of LSP variability change across different luminosity regimes of red giants?

Key findings

• The pulsation period and amplitude, as well as the LSP, increase with increasing luminosity or size of the red giant star.
• The LSP amplitude is largest in moderate-luminosity stars and smaller in both low- and high-luminosity stars.
• The LSP amplitude is particularly small in a sample of 27 Mira stars analyzed using AAVSO visual data.
• The observed trends in LSP amplitude across luminosity classes are consistent with the model in which the LSP is caused by eclipses of the star by a dust-enshrouded companion.
• The increasing LSP and pulsation periods with stellar size support the evolutionary trend of increasing stellar radius with luminosity.
• The complex behavior of LSP amplitude suggests a non-monotonic dependence on stellar evolution, possibly due to changes in dust distribution or orbital geometry in binary systems.