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A study of Galactic Plane Planck Galactic cold clumps observed by SCOPE and the JCMT Plane SurveyWe have investigated the physical properties of Planck Galactic Cold Clumps (PGCCs) located in the Galactic Plane, using the JCMT Plane Survey (JPS) and the SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. By utilizing a suite of molecular-line surveys, velocities, and distances were assigned to the compact sources within the PGCCs, placing them in a Galactic context. The properties of these compact sources show no large-scale variations with Galactic environment. Investigating the star-forming content of the sample, we find that the luminosity-to-mass ratio (L/M) is an order of magnitude lower than in other Galactic studies, indicating that these objects are hosting lower levels of star formation. Finally, by comparing ATLASGAL sources that are associated or are not associated with PGCCs, we find that those associated with PGCCs are typically colder, denser, and have a lower L/M ratio, hinting that PGCCs are a distinct population of Galactic Plane sources.
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A 500 pc volume-limited sample of hot subluminous stars. I. Space density, scale height, and population propertiesWe present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 (~77%) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 are sdOBs (~21%), 32 are sdOs (~11%), and 30 are He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram. The remaining sources in the sample include cataclysmic variables, blue horizontal branch stars, hot white dwarfs, and MS stars. We derived the mid-plane density ρ<SUB>0</SUB> and scale height h<SUB>z</SUB> for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech<SUP>2</SUP>). The best-fit values are ρ<SUB>0</SUB> = 5.17 ± 0.33 × 10<SUP>−7</SUP> stars pc<SUP>−3</SUP> and h<SUB>z</SUB> = 281 ± 62 pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to ρ<SUB>0</SUB> = 6.15<SUB>−0.53</SUB><SUP>+1.16</SUP> × 10<SUP>−7</SUP> stars pc<SUP>−3</SUP>. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates. <P />Tables A.1-A.3 are available at the CDS ftp to <A href=https://cdsarc.cds.unistra.fr>cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href=https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/686/A25>https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/686/A25</A>
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Not So Fast, Not So Furious: Just MagneticWD 0810-353 is a white dwarf within the 20 pc volume around the Sun. Using Gaia astrometric distance and proper motions, and a radial velocity derived from Gaia spectroscopy, it has been predicted that this star will pass within 1 pc of the solar system in about 30 kyr. However, WD 0810-353 has been also shown to host a magnetic field with a strength of the order of 30 MG. Its spectrum is therefore not like those of normal DA stars of similar effective temperature. We have obtained and analyzed new polarized spectra of the star around Hα. Our analysis suggests that the visible surface of the star shows two regions of different field strength (~30 and ~45 MG, respectively), and opposite polarity. The spectra do not change over a 4 yr time span, meaning that either the stellar rotation period is no shorter than several decades, or that the field is symmetric about the rotation axis. Taking into account magnetic shift and splitting, we obtain an estimate of the radial velocity of the star (+83 ± 140 km s<SUP>-1</SUP>); we reject both the value and the claimed precision deduced from the Gaia DR3 spectroscopy (-373.7 ± 8.2 km s<SUP>-1</SUP>), and we conclude that there will probably be no close encounter between the solar system and WD 0810-353. We also reject the suggestion that the star is a hypervelocity runaway star, a survivor of a Type Ia supernova explosion. It is just a stellar remnant in the solar neighborhood with a very strong and complex magnetic field.
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Discovery of Magnetically Guided Metal Accretion onto a Polluted White DwarfDynamically active planetary systems orbit a significant fraction of white dwarf stars. These stars often exhibit surface metals accreted from debris disks, which are detected through infrared excess or transiting structures. However, the full journey of a planetesimal from star-grazing orbit to final dissolution in the host star is poorly understood. Here, we report the discovery that the cool metal-polluted star WD 0816–310 has cannibalized heavy elements from a planetary body similar in size to Vesta, and where accretion and horizontal mixing processes have clearly been controlled by the stellar magnetic field. Our observations unveil periodic and synchronized variations in metal line strength and magnetic field intensity, implying a correlation between the local surface density of metals and the magnetic field structure. Specifically, the data point to a likely persistent concentration of metals near a magnetic pole. These findings demonstrate that magnetic fields may play a fundamental role in the final stages of exoplanetary bodies that are recycled into their white dwarf hosts.
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Search for Stellar Companions of Exoplanet Host Stars with AstraLux/CAHA 2.2 mStellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a Lucky Imaging survey of 212 exoplanet host stars performed with AstraLux at the 2.2 m telescope of the Centro Astronómico Hispano en Andalucía. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{\rm per\ cent}$. In total, 33 binary and 10 hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determine the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.
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A study of galactic plane Planck galactic cold clumps observed by SCOPE and the JCMT plane surveyWe have investigated the physical properties of Planck Galactic Cold Clumps (PGCCs) located in the Galactic Plane, using the JCMT Plane Survey (JPS) and the SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. By utilising a suite of molecular-line surveys, velocities and distances were assigned to the compact sources within the PGCCs, placing them in a Galactic context. The properties of these compact sources show no large-scale variations with Galactic environment. Investigating the star-forming content of the sample, we find that the luminosity-to-mass ratio (L/M) is an order of magnitude lower than in other Galactic studies, indicating that these objects are hosting lower levels of star formation. Finally, by comparing ATLASGAL sources that are associated or are not associated with PGCCs, we find that those associated with PGCCs are typically colder, denser, and have a lower L/M ratio, hinting that PGCCs are a distinct population of Galactic Plane sources.
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Modelling Time-dependent Convective Penetration in 1D Stellar EvolutionOne-dimensional stellar evolution calculations produce uncertain predictions for quantities like the age, core mass, core compactness, and nucleosynthetic yields; a key source of uncertainty is the modeling of interfaces between regions that are convectively stable and those that are not. Theoretical and numerical work has demonstrated that there should be numerous processes adjacent to the convective boundary that induce chemical and angular momentum transport, as well as modify the thermal structure of the star. One such process is called convective penetration, wherein vigorous convection extends beyond the nominal convective boundary and alters both the composition and thermal structure. In this work, we incorporate the process of convective penetration in stellar evolution calculations using the stellar evolution software instrument MESA. We implement convective penetration according to the description presented by Anders et al. to to calculate a grid of models from the pre-main sequence to helium core depletion. The extent of the convective penetration zone is self-consistently calculated at each time step without introducing new free parameters. We find both a substantial penetration zone in all models with a convective core and observable differences to global stellar properties such as the luminosity and radius. We present how the predicted radial extent of the penetration zone scales with the total stellar mass, age, and metallicity of the star. We discuss our results in the context of existing numerical and observational studies.
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NGTS-28Ab: a short period transiting brown dwarfWe report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of ~1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ M<SUB>J</SUB>, close to the hydrogen burning limit, and a radius of 0.95 ± 0.05 R<SUB>J</SUB>. We determine the age to be >0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.
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The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementationWEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, saw first light in late 2022. WEAVE comprises a new 2-deg field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959 nm at R ~ 5000, or two shorter ranges at $R\sim 20\, 000$. After summarizing the design and implementation of WEAVE and its data systems, we present the organization, science drivers, and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ~3 million stars and detailed abundances for ~1.5 million brighter field and open-cluster stars; (ii) survey ~0.4 million Galactic-plane OBA stars, young stellar objects, and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ~400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionized gas in z < 0.5 cluster galaxies; (vi) survey stellar populations and kinematics in ${\sim} 25\, 000$ field galaxies at 0.3 ≲ z ≲ 0.7; (vii) study the cosmic evolution of accretion and star formation using >1 million spectra of LOFAR-selected radio sources; and (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.
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Spectroscopic diagnostics of lead stratification in hot subdwarf atmospheresHeavy metal subdwarfs are a class of hot subdwarfs with very high abundances of heavy elements, typically around 10 000 times solar. They include stars, which are strongly enhanced in either lead or zirconium, as well as other elements. Vertical stratification of the enhanced elements, where the element is concentrated in a thin layer of the atmosphere, has been proposed as a mechanism to explain the apparent high abundances. This paper explores the effects of the vertical stratification of lead on the theoretical spectra of hot subdwarfs. The concentration of lead in different regions of the model atmosphere is found to affect individual lines in a broadly wavelength-dependent manner, with the potential for lines to display modified profiles depending on the location of lead enhancement in the atmosphere. This wavelength dependence highlights the importance of observations in both the optical and the UV for determining whether stratification is present in real stars.
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Tracking the motion of a shock along a channel in the low solar coronaContext. Shock waves are excited by coronal mass ejections (CMEs) and large-scale extreme-ultraviolet (EUV) wave fronts and can result in low-frequency radio emission under certain coronal conditions. <BR /> Aims: In this work, we investigate a moving source of low-frequency radio emission as a CME and an associated EUV wave front move along a channel of a lower density, magnetic field, and Alfvén speed in the solar corona. <BR /> Methods: Observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, the Nançay Radio Heliograph (NRH), and the Irish Low Frequency Array (I-LOFAR) were analysed. Differential emission measure maps were generated to determine densities and Alfvén maps, and the kinematics of the EUV wave front was tracked using CorPITA. The radio sources' positions and velocity were calculated from NRH images and I-LOFAR dynamic spectra. <BR /> Results: The EUV wave expanded radially with a uniform velocity of ∼500 km s<SUP>−1</SUP>. However, the radio source was observed to be deflected and appeared to move along a channel of a lower Alfvén speed, abruptly slowing from 1700 km s<SUP>−1</SUP> to 250 km s<SUP>−1</SUP> as it entered a quiet-Sun region. A shock wave with an apparent radial velocity of > 420 km s<SUP>−1</SUP> was determined from the drift rate of the associated Type II radio burst. <BR /> Conclusions: The apparent motion of the radio source may have resulted from a wave front moving along a coronal wave guide or by different points along the wave front emitting at locations with favourable conditions for shock formation.
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EC 19529-4430: SALT identifies the most carbon- and metal-poor extreme helium starEC 19529-4430 was identified as a helium-rich star in the Edinburgh-Cape (EC) Survey of faint-blue objects and subsequently resolved as a metal-poor extreme helium (EHe) star in the Southern African Large Telescope (SALT) survey of chemically peculiar hot subdwarfs. This paper presents a fine analysis of the SALT high-resolution spectrum. EC 19529-4430 has $T_{\rm eff} = 20\, 700 \pm 250$ K, $\log g /{\rm cm\, s^{-2}} = 3.49\pm 0.03$, and an overall metallicity some 1.3 dex below solar; surface hydrogen is $\approx 0.5~{{\ \rm per\ cent}}$ by number. The surface CNO ratio 1:100:8 implies that the surface consists principally of CNO-processed helium and makes EC 19529-4430 the coolest known carbon-poor and nitrogen-rich EHe star. Metal-rich analogues include V652 Her and GALEX J184559.8-413827. Kinematically, its retrograde orbit indicates membership of the Galactic halo. No pulsations were detected in TESS photometry and there is no evidence for a binary companion. EC 19529-4430 most likely formed from the merging of two helium white dwarfs, which themselves formed as a binary system some 11 Gyr ago.
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Predicting the heaviest black holes below the pair instability gapTraditionally, the pair instability (PI) mass gap is located between 50 and 130 M<SUB>⊙</SUB>, with stellar mass black holes (BHs) expected to 'pile up' towards the lower PI edge. However, this lower PI boundary is based on the assumption that the star has already lost its hydrogen (H) envelope. With the announcement of an 'impossibly' heavy BH of 85 M<SUB>⊙</SUB> as part of GW 190521 located inside the traditional PI gap, we realized that blue supergiant (BSG) progenitors with small cores but large hydrogen envelopes at low metallicity (Z) could directly collapse to heavier BHs than had hitherto been assumed. The question of whether a single star can produce such a heavy BH is important, independent of gravitational wave events. Here, we systematically investigate the masses of stars inside the traditional PI gap by way of a grid of 336 detailed MESA stellar evolution models calculated across a wide parameter space, varying stellar mass, overshooting, rotation, semiconvection, and Z. We evolve low Z stars in the range 10<SUP>-3</SUP> < Z/Z<SUB>⊙</SUB> < Z<SUB>SMC</SUB>, making no prior assumption regarding the mass of an envelope, but instead employing a wind mass-loss recipe to calculate it. We compute critical carbon-oxygen and helium core masses to determine our lower limit to PI physics, and we provide two equations for M<SUB>core</SUB> and M<SUB>final</SUB> that can also be of use for binary population synthesis. Assuming the H envelope falls into the BH, we confirm the maximum BH mass below PI is M<SUB>BH</SUB> ≃ 93.3 M<SUB>⊙</SUB>. Our grid allows us to populate the traditional PI gap, and we conclude that the distribution of BHs above the traditional boundary is not solely due to the shape of the initial mass function, but also to the same stellar interior physics (i.e. mixing) that which sets the BH maximum.
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LISA Galactic Binaries with Astrometry from Gaia DR3Galactic compact binaries with orbital periods shorter than a few hours emit detectable gravitational waves (GWs) at low frequencies. Their GW signals can be detected with the future Laser Interferometer Space Antenna (LISA). Crucially, they may be useful in the early months of the mission operation in helping to validate LISA's performance in comparison to prelaunch expectations. We present an updated list of 55 candidate LISA-detectable binaries with measured properties, for which we derive distances based on Gaia Data Release 3 astrometry. Based on the known properties from electromagnetic observations, we predict the LISA detectability after 1, 3, 6, and 48 months using Bayesian analysis methods. We distinguish between verification and detectable binaries as being detectable after 3 and 48 months, respectively. We find 18 verification binaries and 22 detectable sources, which triples the number of known LISA binaries over the last few years. These include detached double white dwarfs, AM CVn binaries, one ultracompact X-ray binary, and two hot subdwarf binaries. We find that across this sample the GW amplitude is expected to be measured to ≈10% on average, while the inclination is expected to be determined with ≈15° precision. For detectable binaries, these average errors increase to ≈50% and ≈40°, respectively.
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The Magnetic Field in the Colliding Filaments G202.3+2.5We observe the magnetic field morphology toward a nearby star-forming filamentary cloud, G202.3+2.5, using James Clerk Maxwell Telescope/POL-2 850 μm thermal dust polarization observations with an angular resolution of 14.″4 (∼0.053 pc). The average magnetic field orientation is found to be perpendicular to the filaments, while showing different behaviors in the four subregions, suggesting various effects from the filaments' collision in these subregions. With the kinematics obtained by the ${{{\rm{N}}}_{2}{\rm{H}}}^{+}$ observation by IRAM, we estimate the plane-of-sky magnetic field strength by two methods, the classical Davis–Chandrasekhar–Fermi (DCF) method and the angular dispersion function (ADF) method, giving B <SUB>pos,dcf</SUB> and B <SUB>pos,adf</SUB> of ∼90 and ∼53 μG. We study the relative importance between the gravity (G), magnetic field (B), and turbulence (T) in the four subregions, and find G > T > B, G ≥ T > B, G ∼ T > B, and T > G > B in the north tail, west trunk, south root, and east wing, respectively. In addition, we investigate the projection effects on the DCF and ADF methods, based on a similar simulation case, and find the 3D magnetic field strength may be underestimated by a factor of ∼3 if applying the widely used statistical B <SUB>pos</SUB>-to-B <SUB>3D</SUB> factor when using the DCF or ADF methods, which may further underestimate/overestimate the related parameters.
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Search for stellar companions of exoplanet host stars with AstraLux/CAHA 2.2 mStellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a lucky imaging survey of 212 exoplanet host stars performed with AstraLux at CAHA 2.2 m. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{{\%}}$. In total, 33 binary and ten hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determined the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.
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On the Scarcity of Dense Cores (n > 10<SUP>5</SUP> cm<SUP>‑3</SUP>) in High-latitude Planck Galactic Cold ClumpsHigh-latitude (∣b∣ > 30°) molecular clouds have virial parameters that exceed 1, but whether these clouds can form stars has not been studied systematically. Using JCMT SCUBA-2 archival data, we surveyed 70 fields that target high-latitude Planck Galactic cold clumps (HLPCs) to find dense cores with density of 10<SUP>5</SUP>–10<SUP>6</SUP> cm<SUP>‑3</SUP> and size of <0.1 pc. The sample benefits from both the representativeness of the parent sample and its coverage of the densest clumps at the high column density end (>1 × 10<SUP>21</SUP> cm<SUP>‑2</SUP>). At an average rms of 15 mJy beam<SUP>‑1</SUP>, we detected Galactic dense cores in only one field, G6.04+36.77 (L183) while also identifying 12 extragalactic objects and two young stellar objects. Compared to the low-latitude clumps, dense cores are scarce in HLPCs. With synthetic observations, the densities of cores are constrained to be n <SUB> c </SUB> ≲ 10<SUP>5</SUP> cm<SUP>‑3</SUP> should they exist in HLPCs. Low-latitude clumps, Taurus clumps, and HLPCs form a sequence where a higher virial parameter corresponds to a lower dense-core detection rate. If HLPCs were affected by the Local Bubble, the scarcity should favor turbulence-inhibited rather than supernova-driven star formation. Studies of the formation mechanism of the L183 molecular cloud are warranted.
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NGTS-28Ab: A short period transiting brown dwarfWe report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterise the system. We find an orbital period of ~1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ M<SUB>J</SUB>, close to the Hydrogen burning limit, and a radius of 0.95 ± 0.05 R<SUB>J</SUB>. We determine the age to be >0.5 Gyr, using model isochrones, which is found to be in agreement with SED fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.
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Rotation plays a role in the generation of magnetic fields in single white dwarfsRecent surveys of close white dwarf binaries as well as single white dwarfs have provided evidence for the late appearance of magnetic fields in white dwarfs, and a possible generation mechanism, a crystallization and rotation-driven dynamo has been suggested. A key prediction of this dynamo is that magnetic white dwarfs rotate, at least on average, faster than their non-magnetic counterparts and/or that the magnetic field strength increases with rotation. Here we present rotation periods of ten white dwarfs within 40 pc measured using photometric variations. Eight of the light curves come from TESS observations and are thus not biased towards short periods, in contrast to most period estimates that have been reported previously in the literature. These TESS spin periods are indeed systematically shorter than those of non-magnetic white dwarfs. This means that the crystallization and rotation-driven dynamo could be responsible for a fraction of the magnetic fields in white dwarfs. However, the full sample of magnetic white dwarfs also contains slowly rotating strongly magnetic white dwarfs which indicates that another mechanism that leads to the late appearance of magnetic white dwarfs might be at work, either in addition to or instead of the dynamo. The fast-spinning and massive magnetic white dwarfs that appear in the literature form a small fraction of magnetic white dwarfs, and probably result from a channel related to white dwarf mergers.
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Predicting the Heaviest Black Holes below the Pair Instability GapTraditionally, the pair instability (PI) mass gap is located between 50 and 130 M<SUB>⊙</SUB>, with stellar mass black holes (BHs) expected to pile up towards the lower PI edge. However, this lower PI boundary is based on the assumption that the star has already lost its hydrogen (H) envelope. With the announcement of an impossibly heavy BH of 85 M<SUB>⊙</SUB> as part of GW 190521 located inside the traditional PI gap, we realised that blue supergiant (BSG) progenitors with small cores but large Hydrogen envelopes at low metallicity (Z) could directly collapse to heavier BHs than had hitherto been assumed. The question of whether a single star can produce such a heavy BH is important, independent of gravitational wave events. Here, we systematically investigate the masses of stars inside the traditional PI gap by way of a grid of 336 detailed MESA stellar evolution models calculated across a wide parameter space, varying stellar mass, overshooting, rotation, semi-convection, and Z. We evolve low Z stars in the range 10<SUP>-3</SUP> < Z/Z<SUB>⊙</SUB> < Z<SUB>SMC</SUB>, making no prior assumption regarding the mass of an envelope, but instead employing a wind mass loss recipe to calculate it. We compute critical Carbon-Oxygen and Helium core masses to determine our lower limit to PI physics, and we provide two equations for M<SUB>core</SUB> and M<SUB>final</SUB> that can also be of use for binary population synthesis. Assuming the H envelope falls into the BH, we confirm the maximum BH mass below PI is M<SUB>BH</SUB> ≃ 93.3 M<SUB>⊙</SUB>. Our grid allows us to populate the traditional PI gap, and we conclude that the distribution of BHs above the gap is not solely due to the shape of the initial mass function (IMF), but also to the same stellar interior physics (i.e. mixing) that which sets the BH maximum.
