Seth Gossage - Academia.edu (original) (raw)

Papers by Seth Gossage

arXiv (Cornell University), Dec 22, 2022

Magnetic braking has a prominent role in driving the evolution of close low mass binary systems a... more Magnetic braking has a prominent role in driving the evolution of close low mass binary systems and heavily influences the rotation rates of low mass F-and later type stars with convective envelopes. Several possible prescriptions that describe magnetic braking in the context of 1D stellar evolution models currently exist. We test four magnetic braking prescriptions against both low mass X-ray binary orbital periods from the Milky Way and single star rotation periods observed in open clusters. We find that data favors a magnetic braking prescription that follows a rapid transition from fast to slow rotation rates, exhibits saturated (inefficient) magnetic braking below a critical Rossby number, and that is sufficiently strong to reproduce ultra compact X-ray binary systems. Of the four prescriptions tested, these conditions are satisfied by a braking prescription that incorporates the effect of high order magnetic field topology on angular momentum loss. None of the braking prescriptions tested are able to replicate the stalled spin down observed in open cluster stars aged 700-1000 Myr or so, with masses 0.8 M .

arXiv (Cornell University), Nov 1, 2022

Young star clusters enable us to study the effects of stellar rotation on an ensemble of stars of... more Young star clusters enable us to study the effects of stellar rotation on an ensemble of stars of the same age and across a wide range in stellar mass and are therefore ideal targets for understanding the consequences of rotation on stellar evolution. We combine MUSE spectroscopy with HST photometry to measure the projected rotational velocities (sin) of 2 184 stars along the split main sequence and on the main sequence turn-off (MSTO) of the 100 Myr-old massive (10 5 M) star cluster NGC 1850 in the Large Magellanic Cloud. At fixed magnitude, we observe a clear correlation between sin and colour, in the sense that fast rotators appear redder. The average sin values for stars on the blue and red branches of the split main sequence are ∼ 100 km s −1 and ∼ 200 km s −1 , respectively. The values correspond to about 25 − 30% and 50 − 60% of the critical rotation velocity and imply that rotation rates comparable to those observed in field stars of similar masses can explain the split main sequence. Our spectroscopic sample contains a rich population of ∼200 fast rotating Be stars. The presence of shell features suggests that 23% of them are observed through their decretion disks, corresponding to a disk opening angle of 15 degrees. These shell stars can significantly alter the shape of the MSTO, hence care should be taken when interpreting this photometric feature. Overall, our findings impact our understanding of the evolution of young massive clusters and provide new observational constraints for testing stellar evolutionary models.

The Astrophysical Journal

The color–magnitude diagrams (CMDs) of intermediate-age star clusters (≲2 Gyr) are much more comp... more The color–magnitude diagrams (CMDs) of intermediate-age star clusters (≲2 Gyr) are much more complex than those predicted by coeval, nonrotating stellar evolution models. Their observed extended main-sequence turnoffs (eMSTOs) could result from variations in stellar age, stellar rotation, or both. The physical interpretation of eMSTOs is largely based on the complex mapping between stellar models—themselves functions of mass, rotation, orientation, and binarity—and the CMD. In this paper, we compute continuous probability densities in three-dimensional color, magnitude, and v e sin i space for individual stars in a cluster’s eMSTO, based on a rotating stellar evolution model. These densities enable the rigorous inference of cluster properties from a stellar model, or, alternatively, constraints on the stellar model from the cluster’s CMD. We use the MIST stellar evolution models to jointly infer the age dispersion, the rotational distribution, and the binary fraction of the Large Ma...

The extended main sequence turn off (eMSTO) has become recognized as a common, yet puzzling featu... more The extended main sequence turn off (eMSTO) has become recognized as a common, yet puzzling feature of stellar populations since its discovery in the Magellanic Clouds a decade ago with the Hubble Space Telescope (HST). The eMSTO revealed that star clusters are much more complex than we had thought, and since then the origin(s) of the eMSTO have been hotly debated. With new synthetic stellar populations computed from the MESA stellar evolution code, we explore two of the leading theories of the eMSTO phenomenon: an extended star formation history and a range of stellar rotation rates. I will discuss our exploration of the combined effects of both scenarios, including for the first time a non-parametric model for the rotation rate distribution. We find that slow rotators comprise bluer colors, and fast rotators redder colors in the MSTO, as recently observed. Major aspects of the cluster morphology can be replicated with a distribution of rotation rates alone, although we cannot curr...

The Astrophysical Journal, 2021

Two magnetic braking models are implemented in MESA for use in the MIST stellar model grids. Star... more Two magnetic braking models are implemented in MESA for use in the MIST stellar model grids. Stars less than about 1.3 solar masses are observed to spin down over time through interaction with their magnetized stellar winds (i.e., magnetic braking). This is the basis for gyrochronology and is fundamental to the evolution of lower-mass stars. The detailed physics behind magnetic braking are uncertain, as are 1D stellar evolution models. Thus, we calibrate our models and compare to data from open clusters. Each braking model tested here is capable of reproducing aspects of the data, with important distinctions; neither fully accounts for the observations. The Matt et al. prescription matches the slowly rotating stars observed in open clusters but tends to overestimate the presence of rapidly rotating stars. The Garraffo et al. prescription often produces too much angular momentum loss to accurately match the observed slow sequence for lower-mass stars but reproduces the bimodal nature...

The Astrophysical Journal, 2019

The extended main sequence turn offs (eMSTOs) of several young to intermediate age clusters are e... more The extended main sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color-magnitude diagram (CMD), paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a non-parametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: non-rotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted V sin i with observations in order to better constrain the physics related to stellar rotation.

Monthly Notices of the Royal Astronomical Society, 2019

We present a detailed study of stellar rotation in the massive 1.5 Gyr old cluster NGC 1846 in th... more We present a detailed study of stellar rotation in the massive 1.5 Gyr old cluster NGC 1846 in the Large Magellanic Cloud. Similar to other clusters at this age, NGC 1846 shows an extended main-sequence turn-off (eMSTO), and previous photometric studies have suggested it could be bimodal. In this study, we use MUSE integral-field spectroscopy to measure the projected rotational velocities (vsin i) of around 140014001400 stars across the eMSTO and along the upper main sequence of NGC 1846. We measure vsin i values up to sim250,rmkm,s−1\sim 250\, {\rm km\, s^{-1}}sim250,rmkm,s−1 and find a clear relation between the vsin i of a star and its location across the eMSTO. Closer inspection of the distribution of rotation rates reveals evidence for a bimodal distribution, with the fast rotators centred around vsini=140,rmkm,s−1v\sin i=140\, {\rm km\, s^{-1}}vsini=140,rmkm,s−1 and the slow rotators centred around vsini=60,rmkm,s−1v\sin i=60\, {\rm km\, s^{-1}}vsini=60,rmkm,s−1. We further observe a lack of fast rotating stars along the photometric binary sequence of NGC 1846, confirming re...

Monthly Notices of the Royal Astronomical Society, 2019

We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 ... more We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At sim900,rmMyr{\sim}900\,\rm {Myr}sim900,rmMyr Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with mesa Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2...

The Astrophysical Journal, 2018

The Hyades, Praesepe, and Pleiades are well studied stellar clusters that anchor important second... more The Hyades, Praesepe, and Pleiades are well studied stellar clusters that anchor important secondary stellar age indicators. Recent studies have shown that main sequence turn off-based ages for these clusters may depend on the degree of rotation in the underlying stellar models. Rotation induces structural instabilities that can enhance the chemical mixing of a star, extending its fuel supply. In addition, rotation introduces a modulation of the star's observed magnitude and color due to the effects of gravity darkening. We aim to investigate the extent to which stellar rotation affects the age determination of star clusters. We utilize the MESA stellar evolution code to create models that cover a range of rotation rates corresponding to Ω/Ω c = 0.0 to 0.6 in 0.1 dex steps, allowing the assessment of variations in this dimension. The statistical analysis package, MATCH, is employed to derive ages and metallicities by fitting our MESA models to Tycho B T , V T and 2MASS J, K s colormagnitude diagrams. We find that the derived ages are relatively insensitive to the effects of rotation. For the Hyades, Praesepe, and Pleiades, we derive ages based on synthetic populations that model a distribution of rotation rates or a fixed rate. Across each case, derived ages tend to agree roughly within errors, near 680, 590, and 110 − 160 Myr for the Hyades, Praesepe, and Pleiades, respectively. These ages are in agreement with Li depletion boundary-based ages and previous analyses that used non-rotating isochrones. Our methods do not provide a strong constraint on the metallicities of these clusters.

arXiv (Cornell University), Dec 22, 2022

Magnetic braking has a prominent role in driving the evolution of close low mass binary systems a... more Magnetic braking has a prominent role in driving the evolution of close low mass binary systems and heavily influences the rotation rates of low mass F-and later type stars with convective envelopes. Several possible prescriptions that describe magnetic braking in the context of 1D stellar evolution models currently exist. We test four magnetic braking prescriptions against both low mass X-ray binary orbital periods from the Milky Way and single star rotation periods observed in open clusters. We find that data favors a magnetic braking prescription that follows a rapid transition from fast to slow rotation rates, exhibits saturated (inefficient) magnetic braking below a critical Rossby number, and that is sufficiently strong to reproduce ultra compact X-ray binary systems. Of the four prescriptions tested, these conditions are satisfied by a braking prescription that incorporates the effect of high order magnetic field topology on angular momentum loss. None of the braking prescriptions tested are able to replicate the stalled spin down observed in open cluster stars aged 700-1000 Myr or so, with masses 0.8 M .

arXiv (Cornell University), Nov 1, 2022

Young star clusters enable us to study the effects of stellar rotation on an ensemble of stars of... more Young star clusters enable us to study the effects of stellar rotation on an ensemble of stars of the same age and across a wide range in stellar mass and are therefore ideal targets for understanding the consequences of rotation on stellar evolution. We combine MUSE spectroscopy with HST photometry to measure the projected rotational velocities (sin) of 2 184 stars along the split main sequence and on the main sequence turn-off (MSTO) of the 100 Myr-old massive (10 5 M) star cluster NGC 1850 in the Large Magellanic Cloud. At fixed magnitude, we observe a clear correlation between sin and colour, in the sense that fast rotators appear redder. The average sin values for stars on the blue and red branches of the split main sequence are ∼ 100 km s −1 and ∼ 200 km s −1 , respectively. The values correspond to about 25 − 30% and 50 − 60% of the critical rotation velocity and imply that rotation rates comparable to those observed in field stars of similar masses can explain the split main sequence. Our spectroscopic sample contains a rich population of ∼200 fast rotating Be stars. The presence of shell features suggests that 23% of them are observed through their decretion disks, corresponding to a disk opening angle of 15 degrees. These shell stars can significantly alter the shape of the MSTO, hence care should be taken when interpreting this photometric feature. Overall, our findings impact our understanding of the evolution of young massive clusters and provide new observational constraints for testing stellar evolutionary models.

The Astrophysical Journal

The color–magnitude diagrams (CMDs) of intermediate-age star clusters (≲2 Gyr) are much more comp... more The color–magnitude diagrams (CMDs) of intermediate-age star clusters (≲2 Gyr) are much more complex than those predicted by coeval, nonrotating stellar evolution models. Their observed extended main-sequence turnoffs (eMSTOs) could result from variations in stellar age, stellar rotation, or both. The physical interpretation of eMSTOs is largely based on the complex mapping between stellar models—themselves functions of mass, rotation, orientation, and binarity—and the CMD. In this paper, we compute continuous probability densities in three-dimensional color, magnitude, and v e sin i space for individual stars in a cluster’s eMSTO, based on a rotating stellar evolution model. These densities enable the rigorous inference of cluster properties from a stellar model, or, alternatively, constraints on the stellar model from the cluster’s CMD. We use the MIST stellar evolution models to jointly infer the age dispersion, the rotational distribution, and the binary fraction of the Large Ma...

The extended main sequence turn off (eMSTO) has become recognized as a common, yet puzzling featu... more The extended main sequence turn off (eMSTO) has become recognized as a common, yet puzzling feature of stellar populations since its discovery in the Magellanic Clouds a decade ago with the Hubble Space Telescope (HST). The eMSTO revealed that star clusters are much more complex than we had thought, and since then the origin(s) of the eMSTO have been hotly debated. With new synthetic stellar populations computed from the MESA stellar evolution code, we explore two of the leading theories of the eMSTO phenomenon: an extended star formation history and a range of stellar rotation rates. I will discuss our exploration of the combined effects of both scenarios, including for the first time a non-parametric model for the rotation rate distribution. We find that slow rotators comprise bluer colors, and fast rotators redder colors in the MSTO, as recently observed. Major aspects of the cluster morphology can be replicated with a distribution of rotation rates alone, although we cannot curr...

The Astrophysical Journal, 2021

Two magnetic braking models are implemented in MESA for use in the MIST stellar model grids. Star... more Two magnetic braking models are implemented in MESA for use in the MIST stellar model grids. Stars less than about 1.3 solar masses are observed to spin down over time through interaction with their magnetized stellar winds (i.e., magnetic braking). This is the basis for gyrochronology and is fundamental to the evolution of lower-mass stars. The detailed physics behind magnetic braking are uncertain, as are 1D stellar evolution models. Thus, we calibrate our models and compare to data from open clusters. Each braking model tested here is capable of reproducing aspects of the data, with important distinctions; neither fully accounts for the observations. The Matt et al. prescription matches the slowly rotating stars observed in open clusters but tends to overestimate the presence of rapidly rotating stars. The Garraffo et al. prescription often produces too much angular momentum loss to accurately match the observed slow sequence for lower-mass stars but reproduces the bimodal nature...

The Astrophysical Journal, 2019

The extended main sequence turn offs (eMSTOs) of several young to intermediate age clusters are e... more The extended main sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color-magnitude diagram (CMD), paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a non-parametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: non-rotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted V sin i with observations in order to better constrain the physics related to stellar rotation.

Monthly Notices of the Royal Astronomical Society, 2019

We present a detailed study of stellar rotation in the massive 1.5 Gyr old cluster NGC 1846 in th... more We present a detailed study of stellar rotation in the massive 1.5 Gyr old cluster NGC 1846 in the Large Magellanic Cloud. Similar to other clusters at this age, NGC 1846 shows an extended main-sequence turn-off (eMSTO), and previous photometric studies have suggested it could be bimodal. In this study, we use MUSE integral-field spectroscopy to measure the projected rotational velocities (vsin i) of around 140014001400 stars across the eMSTO and along the upper main sequence of NGC 1846. We measure vsin i values up to sim250,rmkm,s−1\sim 250\, {\rm km\, s^{-1}}sim250,rmkm,s−1 and find a clear relation between the vsin i of a star and its location across the eMSTO. Closer inspection of the distribution of rotation rates reveals evidence for a bimodal distribution, with the fast rotators centred around vsini=140,rmkm,s−1v\sin i=140\, {\rm km\, s^{-1}}vsini=140,rmkm,s−1 and the slow rotators centred around vsini=60,rmkm,s−1v\sin i=60\, {\rm km\, s^{-1}}vsini=60,rmkm,s−1. We further observe a lack of fast rotating stars along the photometric binary sequence of NGC 1846, confirming re...

Monthly Notices of the Royal Astronomical Society, 2019

We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 ... more We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At sim900,rmMyr{\sim}900\,\rm {Myr}sim900,rmMyr Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with mesa Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2...

The Astrophysical Journal, 2018

The Hyades, Praesepe, and Pleiades are well studied stellar clusters that anchor important second... more The Hyades, Praesepe, and Pleiades are well studied stellar clusters that anchor important secondary stellar age indicators. Recent studies have shown that main sequence turn off-based ages for these clusters may depend on the degree of rotation in the underlying stellar models. Rotation induces structural instabilities that can enhance the chemical mixing of a star, extending its fuel supply. In addition, rotation introduces a modulation of the star's observed magnitude and color due to the effects of gravity darkening. We aim to investigate the extent to which stellar rotation affects the age determination of star clusters. We utilize the MESA stellar evolution code to create models that cover a range of rotation rates corresponding to Ω/Ω c = 0.0 to 0.6 in 0.1 dex steps, allowing the assessment of variations in this dimension. The statistical analysis package, MATCH, is employed to derive ages and metallicities by fitting our MESA models to Tycho B T , V T and 2MASS J, K s colormagnitude diagrams. We find that the derived ages are relatively insensitive to the effects of rotation. For the Hyades, Praesepe, and Pleiades, we derive ages based on synthetic populations that model a distribution of rotation rates or a fixed rate. Across each case, derived ages tend to agree roughly within errors, near 680, 590, and 110 − 160 Myr for the Hyades, Praesepe, and Pleiades, respectively. These ages are in agreement with Li depletion boundary-based ages and previous analyses that used non-rotating isochrones. Our methods do not provide a strong constraint on the metallicities of these clusters.