Discovery of s-process enhanced stars in the LAMOST survey

Norfolk, Brodie J.; Casey, Andrew R.; Karakas, Amanda I.; Miles, Matthew T.; Kemp, Alex J.; Schlaufman, Kevin C.; Ness, Melissa; Ho, Anna Y. Q.; Lattanzio, John C.; Ji, Alexander P.

doi:10.1093/mnras/stz2630

Cited by 11 publications

(10 citation statements)

References 67 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Throughout this work, we will focus on the relatively hot A/F stars. The nature of the cooler Ba-enhanced stars will be explored in an upcoming study (M. Zhang et al 2020, in preparation; see also Norfolk et al 2019).…”

Section: Distribution In the T Effg Log Diagrammentioning

confidence: 99%

Chemically Peculiar A and F Stars with Enhanced s-process and Iron-peak Elements: Stellar Radiative Acceleration at Work

Xiang

Rix

Ting

et al. 2020

ApJ

View full text Add to dashboard Cite

We present 15,000 metal-rich ([Fe/H]>−0.2 dex) A and F stars whose surface abundances deviate strongly from solar abundance ratios and cannot plausibly reflect their birth material composition. These stars are identified by their high [Ba/Fe] abundance ratios ([Ba/Fe]>1.0 dex) in the LAMOST DR5 spectra analyzed by Xiang et al. They are almost exclusively main-sequence and subgiant stars with T eff 6300 K. Their distribution in the Kiel diagram (T effg log ) traces a sharp border at low temperatures along a roughly fixed-mass trajectory (around 1.4 M e ) that corresponds to an upper limit in convective envelope mass fraction of around 10 −4 . Most of these stars exhibit distinctly enhanced abundances of iron-peak elements (Cr, Mn, Fe, Ni) but depleted abundances of Mg and Ca. Rotational velocity measurements from GALAH DR2 show that the majority of these stars rotate slower than typical stars in an equivalent temperature range. These characteristics suggest that they are related to the so-called Am/Fm stars. Their abundance patterns are qualitatively consistent with the predictions of stellar evolution models that incorporate radiative acceleration, suggesting they are a consequence of stellar internal evolution, particularly involving the competition between gravitational settling and radiative acceleration. These peculiar stars constitute 40% of the whole population of stars with mass above 1.5 M e , affirming that "peculiar" photospheric abundances due to stellar evolution effects are a ubiquitous phenomenon for these intermediate-mass stars. This large sample of Ba-enhanced, chemically peculiar A/F stars with individual element abundances provides the statistics to test more stringently the mechanisms that alter the surface abundances in stars with radiative envelopes. Unified AstronomyThesaurus concepts: Am stars (33); Barium stars (135); Chemically peculiar stars (226); Stellar types (1634); Heavy metal stars (705); Chemical abundances (224); Stellar abundances (1577); Stellar diffusion (1593); Stellar processes (1623); Stellar evolution (1599); Radiative processes (2055); S-process (1419)

show abstract

Section: Distribution In the T Effg Log Diagrammentioning

confidence: 99%

Chemically Peculiar A and F Stars with Enhanced s-process and Iron-peak Elements: Stellar Radiative Acceleration at Work

Xiang

Rix

Ting

et al. 2020

ApJ

View full text Add to dashboard Cite

show abstract

“…Throughout this work, we will focus on the relatively hot A/F stars. The nature of the cooler Ba-enhanced stars will be explored in an upcoming study (Zhang et al in prep., see also Norfolk et al 2019).…”

Section: Distribution In the T Eff -Log G Diagrammentioning

confidence: 95%

Chemically peculiar A and F stars with enhanced s-process and iron-peak elements: stellar radiative acceleration at work

Xiang,

Rix,

Ting

et al. 2020

Preprint

View full text Add to dashboard Cite

We present15, 000 metal-rich ([Fe/H] > −0.2 dex) A and F stars whose surface abundances deviate strongly from Solar abundance ratios and cannot plausibly reflect their birth material composition. These stars are identified by their high [Ba/Fe] abundance ratios ([Ba/Fe] > 1.0 dex) in the LAMOST DR5 spectra analyzed by Xiang et al. (2019). They are almost exclusively main sequence and subgiant stars with T eff 6300 K. Their distribution in the Kiel diagram (T eff -log g) traces a sharp border at low temperatures along a roughly fixed-mass trajectory (around 1.4 M ) that corresponds to an upper limit in convective envelope mass fraction of around 10 −4 . Most of these stars exhibit distinctly enhanced abundances of iron-peak elements (Cr, Mn, Fe, Ni) but depleted abundances of Mg and Ca. Rotational velocity measurements from GALAH DR2 show that the majority of these stars rotate slower than typical stars in an equivalent temperature range. These characteristics suggest that they are related to the so-called Am/Fm stars. Their abundance patterns are qualitatively consistent with the predictions of stellar evolution models that incorporate radiative acceleration, suggesting they are a consequence of stellar internal evolution particularly involving the competition between gravitational settling and radiative acceleration. These peculiar stars constitute 40% of the whole population of stars with mass above 1.5 M , affirming that "peculiar" photospheric abundances due to stellar evolution effects are a ubiquitous phenomenon for these intermediate-mass stars. This large sample of Ba-enhanced chemically peculiar A/F stars with individual element abundances provides the statistics to test more stringently the mechanisms that alter the surface abundances in stars with radiative envelopes.

show abstract

“…Li et al (2018;hereafter L18) found 719 barium stars with strong spectral lines in Ba II at 4554 and Sr II at 4077 Å when they identified carbon stars from LAMOST DR4 by using a machine-learning method. Norfolk et al (2019;hereafter N19) reported 895 (out of 454,180 giants) barium giant candidates that were classified into 49 Ba-only, 659 Sr-only, and 49 both Sr-and Ba-enhancement stars from low-resolution spectra of LAMOST DR2. They predicted the stellar parameters and abundances (T eff , g log , [Fe/H], [α/M]) for their 454,180 giant samples based on a training sample that transfers labels from APOGEE to LAMOST by using the machine-learning method.…”

Section: Introductionmentioning

confidence: 99%

Searching for Barium Stars from the LAMOST Spectra Using the Machine-learning Method: I

Guo¹,

Cheng²,

Kong³

et al. 2023

View full text Add to dashboard Cite

Barium stars are chemically peculiar stars that exhibit enhancement of s-process elements. Chemical abundance analysis of barium stars can provide crucial clues for the study of the chemical evolution of the Galaxy. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has released more than 6 million low-resolution spectra of FGK-type stars by Data Release 9, which can significantly increase the sample size of barium stars. In this paper, we used machine-learning algorithms to search for barium stars from low-resolution spectra of LAMOST. We have applied the Light Gradient Boosting Machine (LGBM) algorithm to build classifiers of barium stars based on different features, and build predictors for determining [Ba/Fe] and [Sr/Fe] of barium candidates. The classification with features in the whole spectrum performs best: for the sample with strontium enhancement, Precision = 97.81% and Recall = 96.05%; for the sample with barium enhancement, Precision = 96.03% and Recall = 97.70%. In prediction, [Ba/Fe] estimated from Ba ii line at 4554 Å has smaller dispersion than that from Ba ii line at 4934 Å: MAE4554 Å = 0.07, σ 4554 Å = 0.12. [Sr/Fe] estimated from Sr ii line at 4077 Å performs better than that from Sr ii line at 4215 Å: MAE4077 Å = 0.09, σ 4077 Å = 0.16. A comparison of the LGBM and other popular algorithms shows that LGBM is accurate and efficient in classifying barium stars. This work demonstrated that machine learning can be used as an effective means to identify chemically peculiar stars and determine their elemental abundance.

show abstract

Discovery of s-process enhanced stars in the LAMOST survey

Cited by 11 publications

References 67 publications

Chemically Peculiar A and F Stars with Enhanced s-process and Iron-peak Elements: Stellar Radiative Acceleration at Work

Chemically Peculiar A and F Stars with Enhanced s-process and Iron-peak Elements: Stellar Radiative Acceleration at Work

Chemically peculiar A and F stars with enhanced s-process and iron-peak elements: stellar radiative acceleration at work

Searching for Barium Stars from the LAMOST Spectra Using the Machine-learning Method: I

Contact Info

Product

Resources

About