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 ( $\mathrm{log}g$ ), 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 $0\,\leqslant \,\mathrm{log}g\,\leqslant \,5.5$ , 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 ( http://www.sdss4.org/dr17/mastar/mastar-stellar-parameters/ ).

This paper presents the twentieth data release (DR20) from the Sloan Digital Sky Survey, the third data release of its fifth generation (SDSS-V). SDSS-V is a panoptic spectroscopy survey that is mapping the stars, gas, and galaxies through three scientific programs: the Milky Way Mapper (MWM), the Local Volume Mapper (LVM), and the Black Hole Mapper (BHM). DR20 presents the first optical (BOSS) SDSS-V spectra from southern hemisphere for the MWM and BHM surveys; new optical MWM and BHM data from the northern hemisphere are also available, for a total over 3 million spectra of 1.5 million stars and half a million galaxies and quasars, with galactic and extragalactic x-ray targets coordinate with eROSITA DR2. DR20 includes integral field spectroscopy maps from LVM of six targets and 169 tiles, spanning Galactic HII regions, planetary nebulae, and nearby galaxies. Additionally, eighteen value added catalogs are also released with DR20, based on SDSS-V MWM and BHM data, and we present a new LVM visualization tool including an RGB HiPS map as a value added product.

Analyses of integral field unit data are typically performed on a per-spaxel basis, with each spectrum modelled independently. For low signal-to-noise ratio (S/N) features such as weak emission lines, estimating properties is difficult and imprecise. Arbitrary binning schemes boost S/N at the cost of resolution, and risk introducing biases. We present a general forward-modeling approach that assumes spectra close on the sky are more similar than distant ones, and so can be modelled jointly. These “spectrospatial” models exploit spatial correlation to provide robust inferences, while simultaneously providing continuous predictions of line properties like strength and kinematics across the sky. Instrumental and calibration systematics are straightforward to include and infer. The model provides a natural trade-off between spatial resolution and S/N in a data-driven way. We apply this to Sloan Digital Sky Survey V Local Volume Mapper (LVM) data of the Rosette Nebula, producing continuous maps of fluxes and kinematics for Balmer, nebular, and auroral lines, as well as weak C ii and N ii recombination lines, demonstrating the approach across 3 orders of magnitude in S/N, including in the very low-S/N regime. The method recovers identical morphologies across different lines tracing similar ionisation volumes, at varying resolutions set by the S/N. We additionally provide a general framework for building and fitting such models in JAX , suitable for many applications. The implementation is fast and memory efficient, scales to large data volumes as in LVM, and can be deployed on hardware accelerators.

The Milky Way Mapper program in the fifth generation of the Sloan Digital Sky Survey (SDSS-V/MWM) has observed millions of stars, thousands of them in open clusters. The Open Cluster Chemical Abundances and Mapping (OCCAM) survey continues to create comprehensive datasets of open clusters and their members in order to constrain Galactic parameters. This eleventh contribution from the OCCAM survey is the first to use stellar parameters from stars observed with the optical Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph to determine cluster membership. We use data from SDSS-V/MWM's 20th Data Release (DR20) and curate a sample of 1883 stars in 111 open clusters, including 95 not in previous OCCAM samples based on infrared data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph. The sample includes 16 clusters with stars observed using both the BOSS and APOGEE spectrographs, and we find consistent agreement in measurements of both [Fe/H] and [α/M]. The BOSS sample includes the majority of the clusters at young ages (Age < 150 Myr) that complement the APOGEE sample of primarily older clusters. We use the combined BOSS+APOGEE OCCAM sample to constrain the radial metallicity gradient with respect to R_guide (-0.079 ± 0.005 dex kpc^-1) and R_gc (-0.082 ± 0.006 dex kpc^-1), which agree well with results from previous OCCAM papers using only APOGEE data. Finally, the inclusion of the primarily young BOSS clusters has not changed that the OCCAM open cluster sample indicates no significant evolution of this gradient in different mono-age populations.

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 <0.4 au and the power-law index of the initial separation distribution 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 O2+ 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 O2+ abundance in an H ii region. These measurements enable construction of the first spatially resolved ADF(O2+) map of an H ii region and yield a global mean ADF of similar to 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 similar to 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 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 use 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 allows us to precisely map ω Cen's line-of-sight rotation out to ∼ 3r_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 show explicitly 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 verify that the SDSS-V's LVM reduction pipeline recovers integrated stellar fluxes to 1-4

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.

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 1-D LTE 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 ⟨[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, which are based on the Hargreaves et al. (2010) line list.

The Sloan Digital Sky Survey V (SDSS-V) is pioneering panoptic spectroscopy: it is the first all-sky, multiepoch, optical-to-infrared spectroscopic survey. SDSS-V is mapping the sky with multiobject spectroscopy (MOS) at telescopes in both hemispheres (the 2.5 m Sloan Foundation Telescope at Apache Point Observatory and the 100-inch du Pont Telescope at Las Campanas Observatory), where 500 zonal robotic fiber positioners feed light from a wide-field focal plane to an optical (R similar to 2000, 500 fibers) and a near-infrared (R similar to 22,000, 300 fibers) spectrograph. In addition to these MOS capabilities, the survey is pioneering ultra-wide-field (similar to 4000 deg(2)) integral field spectroscopy enabled by a new dedicated facility (LVM-I) at Las Campanas Observatory, where an integral field spectrograph (IFS) with 1801 lenslet-coupled fibers arranged in a 0 degrees.5-diameter hexagon feeds multiple R similar to 4000 optical spectrographs that cover 3600-9800 angstrom. SDSS-V's hardware and multiyear survey strategy are designed to decode the chemodynamical history of the Milky Way and tackle fundamental open issues in stellar physics in its Milky Way Mapper program, trace the growth physics of supermassive black holes in its Black Hole Mapper program, and understand the self-regulation mechanisms and the chemical enrichment of galactic ecosystems at the energy injection scale in its Local Volume Mapper program. The survey is well timed to multiply the scientific output from major all-sky space missions. The SDSS-V MOS programs began robotic operations in 2021; IFS observations began in 2023 with the completion of the LVM-I facility. SDSS-V builds on decades of heritage of SDSS's pioneering advances in data analysis, collaboration spirit, infrastructure, and product deliverables in astronomy.

The evolutionary history of the Milky Way disk is imprinted in the ages, positions, and chemical compositions of individual stars. In this study, we derive the intrinsic density distribution of different stellar populations using the final data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. A total of 203,197 red giant branch stars are used to sort the stellar disk (R <= 20 kpc) into subpopulations of metallicity (Delta[M/H] = 0.1 dex), age ( Delta log(ageyr)=0.1 ), and alpha-element abundances ([alpha/M]). We fit the present-day structural parameters and density distribution of each stellar subpopulation after correcting for the survey selection function. The low-alpha disk is characterized by longer scale lengths and shorter scale heights, and is best fit by a broken exponential radial profile for each population. The high-alpha disk is characterized by shorter scale lengths and larger scale heights, and is generally well-approximated by a single exponential radial profile. These results are applied to produce new estimates of the integrated properties of the Milky Way from early times to the present day. We measure the total stellar mass of the disk to be 5.27-1.5+0.2x1010 M circle dot, and the average mass-weighted scale length is Rd = 2.37 +/- 0.2 kpc. The Milky Way's present-day color of (g - r) = 0.72 +/- 0.02 is consistent with the classification of a red spiral galaxy, although it has only been in the "green valley" region of the galaxy color-mass diagram for the last similar to 3 Gyr.

The Rosette Nebula is a well-known HII region shaped by the interaction of gas with the OB stars of the NGC 2244 stellar association. Located within the remnant of a giant molecular cloud, it exhibits a complex structure of ionized gas, molecular material, dust, and embedded clusters. In 2023 October, the region was observed as part of the Sloan Digital Sky Survey V (SDSS-V) local volume mapper (LVM) integral field spectroscopy survey. Covering a radius of similar to 1(degrees), the data set comprises 33 326 spectra with spatially resolved information spanning 390-980 nm. We present a structural analysis of the ionized, molecular, and dusty components using multiwavelength observations: optical spectroscopy from SDSS-V LVM, (CO)-C-12 emission from PMO/MWISP (submillimetre), and dust emission from Widefield Infrared Survey Explorer (12 mu m ) and Herschel (far-infrared). These data sets were complemented with the positions of ionizing stars to study emission structures traced by H alpha, H beta, [O III ], [N II ], and [S II ] as well as the spatial distribution of line ratios (H alpha/H beta, [O III]/H beta, [N II]/H alpha, and [S II]/H alpha) relative to the surrounding molecular cloud. Our analysis reveals interaction zones between ionized and neutral gas, including filaments, globules, and dense regions with or without ongoing star formation. Radial and quadrant-based flux profiles further highlight morphological and ionization variations, supporting the scenario in which the Rosette Nebula evolved from a non-homogeneous molecular cloud with a thin, sheet-like structure.

SDSS-V is the fifth generation of the Sloan Digital Sky Survey and is an ambitious follow-up to a project that has been producing ground-breaking science for more than two decades. SDSS-V uses two dedicated 2.5 m telescopes—the SDSS telescope at Apache Point Observatory in New Mexico and the du Pont telescope at Las Campanas Observatory in Chile—feeding the BOSS and APOGEE spectrographs at each site. These survey machines generate multiobject, all-sky spectroscopy in the optical and near-infrared in support of primary science programs. The new wide-field corrector for the SDSS 2.5 m telescope is one of several major infrastructure upgrades undertaken for SDSS-V, necessitated by the replacement of the legacy fiber plug plate system with a new robotic Focal Plane System (FPS), which places different requirements on the focal characteristics of the telescope. The original two-element corrector produced a focal surface that was nontelecentric and suffered from axial color, throughput, and image quality issues when used in the H band with the APOGEE spectrograph. We have designed and built a three-element fused silica corrector that addresses the optical shortcomings in relation to the FPS. This paper discusses the optical and optomechanical design details of the new wide-field corrector, provides a detailed description of the assembly, integration, and test effort, and concludes with a description of the commissioning effort and on-sky performance.

We introduce the data analysis pipeline (DAP) for the Sloan Digital Sky Survey V Local Volume Mapper (LVM) project, referred to as the LVM-DAP. We outline our methods for recovering both stellar and emission-line components from optical integral field spectroscopy, highlighting the developments and changes implemented to address specific challenges of the data set. The observations from the LVM project are unique because they cover a wide range of physical resolutions, from approximately 0.05 pc to 100 pc, depending on the distance to the target. This, along with the varying number of stars sampled in each aperture (ranging from zero, just one to a few, to thousands), presents challenges in using previous spectral synthesis methods and interpreting the spectral fits. We provide a detailed explanation of how we model the stellar content and separate it from the ionized gas emission lines. To assess the accuracy of our results, we compare them with both idealized and more realistic simulations, highlighting the limitations of our methods. We find that the DAP robustly corrects for stellar continuum features and recovers emission-line parameters (e.g., flux, equivalent width, systemic velocity, and velocity dispersion) with precision and accuracy that fulfill the requirements of the primary goal of the analysis. In addition, the recovered stellar parameters are reliable for single stars, while the recovery of integrated populations is less precise. We conclude with a description of the data products we provide, instructions for downloading and using our software, and a showcase illustrating the quality of the data and the analysis on a deep exposure taken on the Huygens region at the center of the Orion Nebula.

We present one of the largest uniform optical spectroscopic surveys of X-ray selected sources to date that were observed as a pilot study for the Black Hole Mapper (BHM) survey. The BHM program of the Sloan Digital Sky Survey (SDSS)-V is designed to provide optical spectra for hundreds of thousands of X-ray selected sources from the SRG/eROSITA all-sky survey. This significantly improves our ability to classify and characterise the physical properties of large statistical populations of X-ray emitting objects. Our sample consists of 13 079 sources in the eROSITA eFEDS performance verification field, 12 011 of which provide reliable redshifts from 0 less than or similar to z <= 5.8. The vast majority of these objects were detected as point-like sources (X-ray flux limit F0.5 - 2 keV greater than or similar to 6.5 x 10(-15) erg/s/cm(2)) and were observed for about 20 years with fibre-fed SDSS spectrographs. After including all available redshift information for the eFEDS sources from the dedicated SDSS-V plate programme and archival data, we visually inspected the SDSS optical spectra to verify the reliability of these redshift measurements and the performance of the SDSS pipeline. The visual inspection allowed us to recover reliable redshifts (for 99% of the spectra with a signal-to-noise ratio of > 2) and to assign classes to the sources, and we confirm that the vast majority of our sample consists of active galactic nuclei (AGNs). Only similar to 3% of the eFEDS/SDSS sources are Galactic objects. We analysed the completeness and purity of the spectroscopic redshift catalogue, in which the spectroscopic completeness increases from 48% (full sample) to 81% for a cleaner, brighter (r(AB) < 21.38) sample that we defined by considering a high X-ray detection likelihood, a reliable counterpart association, and an optimal sky coverage. We also show the diversity of the optical spectra of the X-ray selected AGNs and provide spectral stacks with a high signal-to-noise ratio in various sub-samples with different redshift and optical broad-band colours. Our AGN sample contains optical spectra of (broad-line) quasars, narrow-line galaxies, and optically passive galaxies. It is considerably diverse in its colours and in its levels of nuclear obscuration.

Dusty disks around planetary and substellar companions in outer reaches of exo-planetary systems can be detected as long-lasting occultations, provided the observer is close to the secondary's orbital plane. Here we report optical spectroscopy with KOSMOS (APO), MagE (Magellan) and GHOST (Gemini-S) of ASASSN-24fw (Gaia 07:05:18.97+06:12:19.4), a 4-magnitude dimming event of a main-sequence star which lasted 8.5 months. We discover multiple low-ionization metal emission lines with velocity dispersion ≲ 10 km/s blue-shifted by 27 km/s with respect to the star, as well as kinematically complex Na D absorption. If associated with the occulter, these detections suggest that the occulter is gas-rich. Further, we detect blue-shifted and broad (∼ 200 km/s) Hα line, which likely originates in the inner circumstellar disk. We confirm the previously reported occultations in 1981 and 1937 seen in historic data, yielding a semi-major axis of the occulter's orbital motion around the star of 14 AU. If the occulter is a circumsecondary disk filling 30-100

We describe a novel framework to model galaxy spectra with two cospatial stellar populations, such as may represent a bulge and bar or thick and thin disc, and apply it to APOGEE spectra in the inner similar to 2 kpc of M31, as well as to stacked spectra representative of the northern and southern parts of M31's disc ( R similar to 4-7 kpc). We use a new unWISE-based photometric decomposition of M31 that includes a Sersic bulge, bar, and exponential disc. This informs our full-spectrum fitting with A-LIST spectral templates to derive the radial velocity, velocity dispersion, metallicity, and alpha abundance for both components in each spectrum. In the bulge, one component exhibits little net rotation, high velocity dispersion (similar to 170 km s(-1)), an average [M/H] = 0.07, and average [alpha/M] = 0.29, while the second component shows structured rotation, lower velocity dispersion (similar to 121 km s(-1)), and similar average abundances. We also constrain the abundance gradients for each of these components. We tentatively associate the first component with the classical bulge and the second with the bar. In the north disc we identify two distinct components: the first with hotter kinematics, lower metallicity, and higher alpha abundance than the second ([M/H] = 0.1 and 0.39, [alpha/M] = 0.29 and 0.07). These discs appear comparable to the Milky Way's 'thick' and 'thin' discs, providing the first evidence that M31's inner disc has a similar chemodynamical structure. Such multipopulation analysis is crucial to constrain galaxy evolution models that strive to recreate the complex stellar populations found in the Milky Way.

We present a first large-scale kinematic map of similar to 50 000 young OB stars (T-eff >= 10 000 K), based on BOSS spectroscopy from the Milky Way Mapper OB programme in the ongoing Sloan Digital Sky Survey V (SDSS-V). Using photogeometric distances, line-of-sight velocities, and Gaia DR3 proper motions, we mapped 3D galactocentric velocities across the Galactic plane to similar to 5 kpc from the Sun, with a focus on radial motions (v(R)). Our results reveal mean radial motion with amplitudes of +/- 30 km/s that are coherent on kiloparsec scales, alternating between inward and outward motions. These (v) over bar (R) amplitudes are considerably higher than those observed for older red-giant populations. These kinematic patterns show only a weak correlation with spiral arm over-densities. Age estimates, derived from MIST isochrones, indicate that 85% of the sample is younger than similar to 300 Myr and that the youngest stars (<= 30 Myr) align well with density enhancements. The age-dependent (v) over bar (R) in Auriga makes it plausible that younger stars exhibit different velocity variations than older giants. The origin of the radial-velocity features remains uncertain, and it may result from a combination of factors, including spiral-arm dynamics, the Galactic bar, resonant interactions, or phase mixing following a perturbation. The present analysis is based on approximately one-third of the full target sample. The completed survey will enable a more comprehensive investigation of these features and a detailed dynamical interpretation.

We present the results of an investigation of a highly variable CIV broad absorption-line feature in the quasar SBS 1408+544 (z=2.337) that shows a significant shift in velocity over time. This source was observed as a part of the Sloan Digital Sky Survey Reverberation Mapping Project and the SDSS-V Black Hole Mapper Reverberation Mapping Project, and has been included in two previous studies, both of which identified significant variability in a high-velocity CIV broad absorption line (BAL) on timescales of just a few days in the quasar rest frame. Using  130 spectra acquired over eight years of spectroscopic monitoring with SDSS, we have determined that this BAL is not only varying in strength, but is also systematically shifting to higher velocities. Using cross-correlation methods, we measure the velocity shifts (and corresponding acceleration) of the BAL on a wide range of timescales, measuring an overall velocity shift of delta v = -683 (+89, -84) km s-1 over the 8-year monitoring period. This corresponds to an average rest-frame acceleration of a=1.04 (+0.14, -0.13) cm s-2, though the magnitude of the acceleration on shorter timescales is not constant throughout. We place our measurements in the context of BAL-acceleration models and examine various possible causes of the observed velocity shift.

We present the results of an investigation of a highly variable C iv broad absorption line (BAL) feature in spectra of the quasar SBS 1408+544 (z = 2.337) that shows a significant shift in velocity over time. This source was observed as a part of the Sloan Digital Sky Survey (SDSS) Reverberation Mapping project and the SDSS-V Black Hole Mapper Reverberation Mapping project, and has been included in two previous studies, both of which identified significant variability in a high-velocity C iv BAL on timescales of just a few days in the quasar rest frame. Using similar to 130 spectra acquired over 8 yr of spectroscopic monitoring with SDSS, we have determined that this BAL is not only varying in strength, but is also systematically shifting to higher velocities. Using cross-correlation methods, we measure the velocity shifts (and corresponding acceleration) of the BAL over a wide range of timescales, measuring an overall velocity shift of Delta v = -683(-84 )(+ 89) km s(-1) over the 8 yr monitoring period. This corresponds to an average rest-frame acceleration of a = 1.04(-0.13)(+0.14) cm s(-2), though the magnitude of the acceleration on shorter timescales is not constant throughout. We place our measurements in the context of BAL-acceleration models and examine various possible causes of the observed velocity shift.