Dmitry Bizyaev

The Sloan Digital Sky Survey (SDSS)-V Local Volume Mapper (LVM) is a wide-field integral field spectroscopic survey of the southern Milky Way plane, the Magellanic Clouds, and nearby Local Group galaxies. We used early science observations of the whole body of the nearest nuclear cluster, Omega Centauri, to extend the LVM beyond its primary interstellar-medium science case. The wide LVM field allowed us to precisely map ω Cen’s line-of-sight rotation out to ~3 r _HL or 15′, reaching a maximum value of (8.4 ± 0.8) km s ⁻¹ at r ≈ 4.7′. Within the central region, comparisons with existing VLT MUSE oMEGACat data explicitly show that the unresolved light signal is dominated by a small number of bright stars, with an effective sample size of only ~12 per resolution element. Using Gaia DR3 as an external reference, we verified that the SDSS-V’s LVM reduction pipeline recovers integrated stellar fluxes to 1–4% across six magnitudes of surface brightness. Our resulting total spectrum of ω Cen is one of the highest S/N integrated spectra for any globular or nuclear star cluster. We used it to test four widely used SSP template libraries against the resolved age-metallicity ground truth from oMEGACat. All templates recovered an old, metal-poor population. However, even at signal to noise ratio of ~1300, the inferred mean ages and mean [Fe/H] vary by ~7 Gyr and ~0.4 dex, respectively, across libraries and wavelength ranges, reflecting a systematic floor for integrated-light studies of old multi-population systems.

We present the stellar parameters for 59,266 high-quality spectra of 24,130 unique stars from the MaNGA Stellar Library (MaStar) in the Sloan Digital Sky Survey (SDSS) Data Release 17 (DR17). The median signal-to noise ratio per pixel of the spectra is 96. We derive four stellar parameters, effective temperature ( T _eff ), surface gravity ( log g ), metallicity ([M/H]), and α -enhancement ratio ([ α /M]), by comparing the data with BOSZ (ATLAS-9 based) and MARCS theoretical atmospheric models. We adopt a Bayesian method and use color and absolute magnitude derived from Gaia to select a subset of theoretical models for each star. We then perform full-spectrum fitting to estimate the likelihood of each model in the subset and then compute their likelihood-weighted mean parameters as the final parameters. We set stellar-parameter quality flags to facilitate the use of the derived stellar parameters. The MaStar stellar parameters derived herein span an effective temperature range of 2600 ≤ T _eff ≤ 29,861 K, a surface gravity range of 0 ≤ log g ≤ 5.5 , a metallicity range of −4.9 ≤ [M/H] ≤ 1.0, and an α -abundance range of −0.98 ≤ [ α /M] ≤ 1.0. We compare these parameters with those from APOGEE and Gaia for stars in common, finding general consistency within the uncertainties. However, some artifacts and systematic differences are present, and we discuss their potential causes. These new stellar parameters are available through the MaStar SDSS-IV DR17 value-added catalog ( https://www.sdss4.org/dr17/mastar/mastar-stellar-parameters/ ).

Recent studies have suggested a mismatch of up to 0.20 dex between iron abundances derived from Fe I and FeH lines in the H -band spectra of M dwarfs and in this work we investigate the nature of this possible offset. We analyze near-infrared H -band APOGEE spectra of stars in 18 binaries composed of a G dwarf primary and an M dwarf secondary, together with four M dwarf stars having measured angular diameters from the literature, and six M dwarf members of the Hyades and Coma Berenices open clusters. These three families of benchmarks were used to evaluate the FeH line list and check for possible systematic uncertainties in the FeH gf -values. Our tests used 1D local thermodynamic equilibrium plane-parallel model atmospheres, a radiative transfer code, and the baseline APOGEE spectral line list to derive metallicities for the binary G dwarf primaries using Fe I lines, while stellar parameters and metallicities for the M dwarfs used both FeH and Fe I lines. The mean metallicity obtained for the Hyades M dwarfs was 〈[Fe/H]〉 = +0.08 ± 0.04, and for Coma Berenices it was 〈[Fe/H]〉 = +0.02 ± 0.08. The metallicities of the G and M dwarfs in binary systems showed excellent agreement (0.06 dex), and the mean metallicities for the open clusters were also consistent with literature values from high-resolution optical analyses. We investigated the consistency between the spectroscopic and interferometric T _eff scales, finding agreement within the uncertainties. Forcing full agreement between the spectroscopic and interferometric T _eff scales resulted in a poorer match for the metallicities in the binaries and the open clusters. We conclude that the best overall concordance is obtained when no adjustments are made to the FeH gf -values that are based on the R. J. Hargreaves et al. line list.

Mapping the local and distant Universe is key to our understanding of it. For decades, the Sloan Digital Sky Survey (SDSS) has made a concerted effort to map millions of celestial objects to constrain the physical processes that govern our Universe. The most recent and fifth generation of SDSS (SDSS-V) is organized into three scientific “mappers”: the Milky Way Mapper, which aims to chart the various components of the Milky Way and constrain its formation and assembly; the Black Hole Mapper, which focuses on understanding supermassive black holes in distant galaxies across the Universe; and the Local Volume Mapper, which uses integral field spectroscopy to map the ionized interstellar medium in the Local Group. This paper describes the scope and content for the nineteenth data release (DR19) of SDSS, which is the most substantial to date in SDSS-V. DR19 is the first to contain data from all three mappers. Additionally, we also describe nine value-added catalogs that enhance the science that can be conducted with the SDSS-V data. Finally, we discuss how to access SDSS DR19 and provide illustrative examples and tutorials.

The so-called “Galactic center lobe” (GCL) is an extended (~1°) radio continuum feature situated above the Galactic plane, the nature and location of which have been subject to varying claims in the literature. Using new optical integral field spectroscopic observations from the SDSS-V Local Volume Mapper, we confirm the characterization of the GCL as a foreground photoionized H II region, not associated with the Galactic center. We present a new analysis of the ionized gas morphology, line ratio diagnostics, and kinematics. From our [S III ] λ 9532 emission line map, which suffers the least extinction, we identify ionized gas emission throughout a closed outer loop, which does not fill the GCL interior. All optical line ratio diagnostics are consistent with photoionization. By comparing the ionized gas reddening from the Balmer decrement with 3D dust maps, we directly constrain the distance to the GCL to ~2 kpc. [N II ] λ 6583 line kinematics show a uniform velocity structure across the GCL, further confirming that the entire bubble is one structure. The size and emission line morphology is strongly reminiscent of that seen in the nearby Barnard’s Loop, providing a possible analog to explain how this outer shell may be photoionized by a more distant and off-center embedded young cluster. We suggest that the acronym GCL be repurposed to instead abbreviate the name “greatly confused loop”.

The fifth-generation Sloan Digital Sky Survey (SDSS-V) includes the first large-scale spectroscopic survey of white dwarfs (WDs) in the era of Gaia parallaxes. SDSS-V collects multiple exposures per target, making it ideal for binary detection. We present a search for hydrogen atmosphere (DA) double WD (DWD) binaries in this rich dataset. We quantify radial velocity variations between subexposures to identify binary candidates, and we measure the orbital period for a subset of DWD binary candidates. We find 60 DWD binary candidates, of which 43 are new discoveries, and report tentative periods for 9 of these binaries. From these binary candidates, we derive a Galactic WD binary fraction f _bin,0.4 = 9% for binary separations α = −0.62. Using the simulated binary population, we find that approximately two to five super-Chandrasekhar-mass binaries that merge within a Hubble time are expected in our sample at a 95% confidence interval. We predict that approximately two systems in our sample should be detectable via gravitational waves by the Laser Interferometer Space Antenna (LISA), one of which has already been identified as a LISA verification source. We also estimate a total of about 10,000–20,000 LISA-detectable DWD binaries in the Galaxy. Our catalog of WD+WD binary candidates in SDSS-V is now public and promises to uncover a large number of exciting DWD systems.

The abundance discrepancy problem refers to the systematic differences observed between chemical abundances derived from collisionally excited lines (CELs) and recombination lines (RLs) of heavy ions. It remains a major unsolved problem in the study of ionized nebulae and is quantified by the abundance discrepancy factor (ADF). In this work, we present a deep integral field spectroscopic data set of the entire Lagoon Nebula (M8), obtained by the Sloan Digital Sky Survey V Local Volume Mapper project, at a spatial resolution of 0.21 pc spaxel ⁻¹ . This unique data set allows us, for the first time, to investigate spatially resolved maps of oxygen RL intensities (O ii V1), together with maps of H i RLs, heavy-ion CELs, and dust attenuation across a whole H ii region. We map the electron temperature using CELs and RLs of O ²⁺ and CELs of N ⁺ , and we map the electron density using CELs of S ⁺ . We derive CEL-based ionic and elemental oxygen abundances and, for the first time, a spatially resolved map of the RL-based O ²⁺ abundance in an H ii region. These measurements enable construction of the first spatially resolved ADF(O ²⁺ ) map of an H ii region and yield a global mean ADF of ∼0.47 ± 0.02 dex. Focusing on the central region of M8, where ionization is dominated by the O-type star Her 36, we find radial variations in the ADF, ranging between ∼0.35 and 0.50 dex. Our findings provide novel constraints on the spatial behavior and origin of the abundance discrepancy in the H ii regions.

The Milky Way bulge bar is composed of multiple populations. Using chemical and kinematical planes, we segregate six populations in a bulge bar sample observed by the APOGEE survey: two with bar-driven orbits, two with eccentric orbits, and two with low-eccentricity orbits, each composed of low- and high-[Mg/Fe] stars. Our sample spans −2.0 ≲ [Fe/H] ≲ +0.5 and Galactocentric distance R _Gal < 6 kpc. We use chemical abundances from APOGEE DR17 for the elements Mg, Si, Ca, Al, K, Mn, Co, Ni, and Fe and from the BAWLAS catalog for Ce and Nd. We find that the low- and high-[Mg/Fe] stars with low-eccentricity orbits, which exhibit chemical and orbital characteristics similar to those of the low- and high-[ α /Fe] disks, display slightly negative and positive metallicity gradients, respectively. This result for the low-[Mg/Fe], low-eccentricity stars indicates a break in the global thin-disk metallicity gradient. The high-eccentricity populations with both low and high [Mg/Fe] show approximately flat metallicity gradients. In general, the [X/H] gradients of all elements for all populations follow Fe, except for the neutron-capture elements Ce and Nd. For all elements, the high-[Mg/Fe] bar population shows a much steeper positive [X/H] gradient than the nearly flat gradient for the low-[Mg/Fe] bar stars. The positive [X/H] gradients observed among our high-[Mg/Fe] bar stars probably reflect an age variation along the peanut structure. This interpretation agrees with the N -body simulations. Such steep positive gradients have also been reported in some high-redshift ( z ∼ 4–10) galaxies.

Aims . The chemical abundance of the interstellar medium sets the initial conditions for star formation and provides a probe of chemical galaxy evolution models. However, unresolved inhomogeneities in the electron temperature can lead to a systematic underestimation of the abundances. We aim to directly test this effect. Methods . We used the SDSS-V Local Volume Mapper to spatially map the physical conditions of the Trifid Nebula (M 20), a Galactic H II region ionized by a single mid-type O-star, at a 0.24 pc resolution. We exploited various emission lines (e.g., Hydrogen recombination lines and collisionally excited lines, including also faint auroral lines) and computed the spatially resolved maps of [O II ] and [S II ] electron densities, the [N II ], [O II ], [S II ], and [S III ] electron temperatures, and the ionic oxygen abundances. Results . We found internal variations of electron density that result from the ionization front, along with a negative radial gradient. However, we did not find any strong gradients or structures in the electron temperature and the total oxygen abundance, making the Trifid Nebula a relatively homogeneous H II region at the observed spatial scale. We compared these spatially resolved properties with equivalent integrated measurements of the Trifid Nebula and found no significant variations between integrated and spatially resolved conditions. Conclusions . This isolated H II region, ionized by a single O-star, represents a test case of an ideal Strömgren sphere. The physical conditions in the Trifid Nebula behave as expected, with no significant differences between integrated and resolved measurements.