Star formation history of the solar neighbourhood as told by Gaia

Abstract

The Gaia DR2 catalog is the best source of stellar astrometric and photometric data available today. The history of the Milky Way galaxy is written in stone in this data set. Parallaxes and photometry tell us where the stars are today, when were they formed, and with what chemical content, i.e. their star formation history (SFH). We develop a Bayesian hierarchical model suited to reconstruct the SFH of a resolved stellar population. We study the stars brighter than G = 15 within 100 pc of the Sun in Gaia DR2 and derive a SFH of the solar neighbourhood in agreement with previous determinations and improving upon them because we detect chemical enrichment. Our results show a maximum of star formation activity about 10 Gyr ago, producing large numbers of stars with slightly below solar metallicity (Z = 0.014), followed by a decrease in star formation up to a minimum level occurring around 8 Gyr ago. After a quiet period, star formation rises to a maximum at about 5 Gyr ago, forming stars of solar metallicity (Z = 0.017). Finally, star formation has been decreasing until the present, forming stars of Z = 0.03 at a residual level. We test the effects introduced in the inferred SFH by ignoring the presence of unresolved binary stars in the sample, reducing the apparent limiting magnitude, and modifying the stellar initial mass function.

Binary evolution pathways of blue large-amplitude pulsators

“…Values have been scaled relative to our reference star formation history and show how the ratio in total number of BLAPs changes with length of the ongoing star formation episode and with the presumed metal enrichment of the disk population. We also show a prediction for the Alzate et al (2021) stepwise stellar population model for the Milky Way as discussed in section 6.2. The dotted line indicates constant star formation for log(age/years)=10.1, while the dashed line assumes the same star formation rate but for just 10 Gyr.…”

“…Stars with these compositions are all present in the disk population (e.g. Alzate et al 2021). The primary star weighting in the population synthesis at each metallicity is identical to that at = 0.020 (we assume no dependence of IMF or binary initial parameters on metal content) but the age at which stars enter the BLAP region of interest, their BLAP lifetimes, their masses and the weightings of secondary models are all calculated from the results of detailed stellar evolution code and so may vary due to metaldependent opacities, winds and other evolutionary processes.…”

“…In the same figure, we also consider a more complex case, in which the Milky Way disk population is modelled as a heterogeneous mix of stars of different metallicity, each metallicity population exhibiting a different star formation history. To do so we adopt the step-wise determination of Milky Way disk star formation history determined from Gaia data by Alzate et al (2021). For each age bin in the star formation history model we identify the closest age bin on the BPASS model grid, and we use their mass fraction estimates as a function of age and metallicity at = 0.010, 0.014, 0.017 (applied to BPASS at = 0.020) and 0.030.…”

Binary evolution pathways of Blue Large-Amplitude Pulsators

“…Stars with these compositions are all present in the disk population (e.g. Alzate et al 2021). The primary star weighting in the population synthesis at each metallicity is identical to that at 𝑍 = 0.020 (we assume no dependence of IMF or binary initial parameters on metal content) but the age at which stars enter the BLAP region of interest, their BLAP lifetimes, their masses and the weightings of secondary models are all calculated from the results of detailed stellar evolution code and so may vary due to metaldependent opacities, winds and other evolutionary processes.…”

“…In the same figure, we also consider a more complex case, in which the Milky Way disk population is modelled as a heterogeneous mix of stars of different metallicity, each metallicity population exhibiting a different star formation history. To do so we adopt the step-wise determination of Milky Way disk star formation history determined from Gaia data by Alzate et al (2021). For each age bin in the star formation history model we identify the closest age bin on the BPASS model grid, and we use their mass fraction estimates as a function of age and metallicity at 𝑍 = 0.010, 0.014, 0.017 (applied to BPASS at 𝑍 = 0.020) and 0.030.…”