A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A*

Gull, Maude; Weisz, Daniel R.; Senchyna, Peter; Sandford, Nathan R.; Choi, Yumi; McLeod, Anna F.; El-Badry, Kareem; Götberg, Y.; Gilbert, Karoline M.; Boyer, Martha L.; Dalcanton, Julianne J.; Guhathakurta, Puragra; Goldman, Steven; Marigo, Paola; McQuinn, Kristen B. W.; Pastorelli, Giada; Stark, Daniel P.; Skillman, Evan D.; Ting, Yuan-Sen; Williams, Benjamin F.

doi:10.3847/1538-4357/aca295

Cited by 6 publications

(5 citation statements)

References 169 publications

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“…They derived a mean [Fe/ H] = −1.67, only slightly below the gas-phase metallicity, suggesting a slow chemical enrichment in Leo A, in agreement with the flat age-metallicity relation derived from Hubble Space Telescope (HST) photometry by Cole et al (2007). More recently, Gull et al (2022) derived stellar parameters for a sample of massive stars (late O/early B main-sequence objects) in Leo A from both HST photometry and ground-based spectroscopy.…”

Section: Introductionsupporting

confidence: 70%

“…We are not aware of published spectra of this ionized nebula. This is star K1/B1 of Gull et al (2022). Nebular contamination is clearly seen at Hβ, as shown by the spectrum in Figure 2, while the twodimensional spectra also show weak extended emission at Hγ.…”

Section: Spectral Classificationmentioning

confidence: 67%

“…We note that, like these authors, we selected the brightest blue stars as candidates for the stellar spectroscopy. However, the brightest star observed by Gull et al (2022) has a B magnitude of 20.1 (in the photometric catalog of Stonkutė et al 2014), while our sample includes, in addition to the object in common mentioned above, seven blue (B − V of around −0.2 to 0.1) stars brighter than this limit.…”

Section: Spectral Classificationmentioning

confidence: 99%

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The Metallicity and Distance of Leo A from Blue Supergiants

Urbaneja,

Bresolin,

Kudritzki

2023

ApJ

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We have obtained high-quality spectra of blue supergiant candidates in the dwarf irregular galaxy Leo A with the Low Resolution Imaging Spectrometer at the Keck I telescope. From the quantitative analysis of seven B8–A0 stars, we derive a mean metallicity [Z] = −1.35 ± 0.08, in excellent agreement with the gas-phase chemical abundance. From the stellar parameters and the flux-weighted gravity–luminosity relation (FGLR), we derive a spectroscopic distance modulus m − M = 24.77 ± 0.11 mag, significantly larger (∼0.4 mag) than the value indicated by RR Lyrae and other stellar indicators. We explain the bulk of this discrepancy with blue loop stellar evolution at very low metallicity and show that the combination of metallicity effects and blue loop evolution amounts, in the case of Leo A, to an ∼0.35 mag offset of the FGLR to fainter bolometric luminosities. We identify one outlier of low bolometric magnitude as a post-AGB star. Its metallicity is consistent with that of the young population, confirming the slow chemical enrichment of Leo A.

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Section: Introductionsupporting

confidence: 70%

Section: Spectral Classificationmentioning

confidence: 67%

Section: Spectral Classificationmentioning

confidence: 99%

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The Metallicity and Distance of Leo A from Blue Supergiants

Urbaneja,

Bresolin,

Kudritzki

2023

ApJ

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“…Examples include the young MS, the RGB and AGB, the HB, and the oldest MSTO. The relative positions of these features are generally similar to what is known for optical CMDs with subtle changes due to the shift to IR wavelengths (e.g., Dalcanton et al 2012b;Williams et al 2014;Gull et al 2022). For example, the HB slopes to fainter values at bluer wavelengths as hot blue HB stars are less luminous at IR wavelengths.…”

Section: Wlmsupporting

confidence: 61%

The JWST Resolved Stellar Populations Early Release Science Program II. Survey Overview

Weisz¹,

McQuinn²,

Savino³

et al. 2023

Preprint

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We present the JWST Resolved Stellar Populations Early Release Science (ERS) science program. We obtained 27.5 hours of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultra-faint dwarf galaxy Draco II, star-forming dwarf galaxy WLM), which span factors of ∼ 10 5 in luminosity, ∼ 10 4 in distance, and ∼ 10 5 in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color-magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen burning limit in M92 (< 0.08 M ; SNR ∼ 5 at m F 090W ∼ 28.2; M F 090W ∼ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 M ; SNR = 10 at m F 090W ∼ 29; M F 090W ∼ +12.1), and reach ∼ 1.5 magnitudes below the oldest main sequence turnoff in WLM (SNR = 10 at m F 090W ∼ 29.5; M F 090W ∼ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though are ∼ 0.05 mag too blue compared to M92 F090W−F150W data. The NIRCam ETC (v2.0) matches the SNRs based on photon noise from DOLPHOT stellar photometry in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for HST. We release beta versions of DOLPHOT NIRCam and NIRISS modules to the community. Results from this ERS program will establish JWST as the premier instrument for resolved stellar populations studies for decades to come.

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“…Examples include the young MS, the RGB and AGB, the HB, and the oldest MSTO. The relative positions of these features are generally similar to what is known for optical CMDs with subtle changes due to the shift to IR wavelengths (e.g.,Dalcanton et al 2012a;Williams et al 2014;Gull et al 2022). For example, the HB slopes to fainter values at bluer wavelengths as hot blue HB stars are less luminous at IR wavelengths.…”

mentioning

confidence: 99%

The JWST Resolved Stellar Populations Early Release Science Program. II. Survey Overview

Weisz,

McQuinn,

Savino

et al. 2023

ApJS

Self Cite

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We present the JWST Resolved Stellar Populations Early Release Science (ERS) program. We obtained 27.5 hr of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultrafaint dwarf galaxy Draco II, and star-forming dwarf galaxy WLM), which span factors of ∼105 in luminosity, ∼104 in distance, and ∼105 in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color–magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen-burning limit in M92 (<0.08 M ⊙; M F090W ∼ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 M ⊙; M F090W ∼ +12.1), and reach ∼1.5 mag below the oldest main-sequence turnoff in WLM (M F090W ∼ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though they are ∼0.05 mag too blue compared to M92 F090W − F150W data. Our CMDs show detector-dependent color offsets ranging from ∼0.02 mag in F090W – F150W to ∼0.1 mag in F277W – F444W; these appear to be due to differences in the zero-point calibrations among the detectors. The NIRCam ETC (v2.0) matches the signal-to-noise ratios based on photon noise in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for the Hubble Space Telescope. We release the point-source photometry package DOLPHOT, optimized for NIRCam and NIRISS, for the community.

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A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A*

Cited by 6 publications

References 169 publications

The Metallicity and Distance of Leo A from Blue Supergiants

The Metallicity and Distance of Leo A from Blue Supergiants

The JWST Resolved Stellar Populations Early Release Science Program II. Survey Overview

The JWST Resolved Stellar Populations Early Release Science Program. II. Survey Overview

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