Proceedings of the International Astronomical Union, 2017
The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new facility led by the High Altitu... more The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new facility led by the High Altitude Observatory and a consortium of partners to measure magnetic field and plasma properties in a large (one degree) field of view extending down to the inner parts of the solar corona. CoSMO is intended as a research facility that will advance the understanding and prediction of space weather. The instrumentation elements of CoSMO are: a white-light coronagraph (KCor), already operational at the Mauna Loa Solar Observatory (MLSO); the Chromosphere and Prominence Magnetometer (ChroMag), due for deployment to MLSO next year; and the CoSMO Large Coronagraph (LC) which has completed Preliminary Design Review.
The Daniel K. Inouye Solar Telescope (DKIST) advances studies of solar magnetism through high-pre... more The Daniel K. Inouye Solar Telescope (DKIST) advances studies of solar magnetism through high-precision and accuracy in polarimetry at frontier spatial and temporal scales. A system model for polarization response in azimuth and altitude has been developed to calibrate DKIST instruments. The DKIST team has developed several new modeling and performance-estimation techniques coupled with thorough metrology. These efforts ensure that quality polarimetry is delivered to meet stringent accuracy requirements. A custom spectropolarimetric calibration system was designed, installed, and used to perform end-to-end calibration of the telescope using the beam within the Cryo-NIRSP instrument. Extensive optical and polarization characterization efforts allow for the reduction of systematic errors within a detailed system model that includes elliptical calibration retarders. Coating witness samples for every relevant optic in the system have been measured. Aperture-dependent variations in polar...
Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospher... more Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospheric physics and sculpting stellar winds. Observations of stellar magnetic fields are typically made in the visible, although infrared observations are becoming common. Here we consider the possibility of directly detecting magnetic fields at ultraviolet (UV) wavelengths using high resolution spectropolarimetry, specifically considering the capabilities of the proposed Polstar mission. UV observations are particularly advantageous for studying wind resonance lines not available in the visible, but they can also provide many photospheric lines in hot stars. Detecting photospheric magnetic fields using the Zeeman effect and Least Squares Deconvolution is potentially more effective in the UV due to the much higher density of strong lines. We investigate detecting magnetic fields in the magnetosphere of a star using the Zeeman effect in wind lines, and find that this could be detectable at high S/N in an O or B star with a strong magnetic field. We consider detecting magnetic fields using the Hanle effect in linear polarization, which is complementary to the Zeeman effect, and could be more sensitive in photospheric lines of rapid rotators. The Hanle effect can also be used to infer circumstellar magnetism in winds. Detecting the Hanle effect requires UV observations, and a multi-line approach is key for inferring magnetic field properties. This demonstrates that high resolution spectropolarimetry in the UV, and the proposed Polstar mission, has the potential to greatly expand our ability to detect and characterize magnetic fields in and around hot stars.
Magnetic fields govern the plasma dynamics in the outer layers of the solar atmosphere, and elect... more Magnetic fields govern the plasma dynamics in the outer layers of the solar atmosphere, and electric fields acting on neutral atoms that move across the magnetic field enable us to study the dynamical coupling between neutrals and ions in the plasma. In order to measure the magnetic and electric fields of chromospheric jets, the full Stokes spectra of the Paschen series of neutral hydrogen in a surge and in some active region jets that took place at the solar limb were observed on May 5, 2012, using the spectropolarimeter of the Domeless Solar Telescope at Hida observatory, Japan. First, we inverted the Stokes spectra taking into account only the effect of magnetic fields on the energy structure and polarization of the hydrogen levels. Having found no definitive evidence of the effects of electric fields in the observed Stokes profiles, we then estimated an upper bound for these fields by calculating the polarization degree under the magnetic field configuration derived in the first step, with the additional presence of a perpendicular (Lorentz type) electric field of varying strength. The inferred direction of the magnetic field on the plane of the sky (POS) approximately aligns to the active region jets and the surge, with magnetic field strengths in the range 10 G < B < 640 G for the surge. Using magnetic field strengths of 70, 200, and 600 G, we obtained upper limits for possible electric fields of 0.04, 0.3, and 0.8 V cm −1 , respectively. This upper bound is conservative, since in our modeling we neglected the possible contribution of collisional depolarization. Because the velocity of neutral atoms of hydrogen moving across the magnetic field derived from these upper limits of the Lorentz electric field is far below the bulk velocity of the plasma perpendicular to the magnetic field as measured by the Doppler shift, we conclude that the neutral atoms must be highly frozen to the magnetic field in the surge.
We present some theoretical predictions concerning the amplitude and magnetic sensitivity of the ... more We present some theoretical predictions concerning the amplitude and magnetic sensitivity of the linear polarization signals produced by scattering processes in the hydrogen Lyα line of the solar transition region. To this end, we have calculated the atomic level polarization (population imbalances and quantum coherences) induced by anisotropic radiation pumping in semi-empirical and hydrodynamical models of the solar atmosphere, taking into account radiative transfer and the Hanle effect caused by the presence of organized and random magnetic fields. The line-center amplitudes of the emergent linear polarization signals are found to vary typically between 0.1% and 1%, depending on the scattering geometry and the strength and orientation of the magnetic field. The results shown here encourage the development of UV polarimeters for sounding rockets and space telescopes with the aim of opening up a diagnostic window for magnetic field measurements in the upper chromosphere and transition region of the Sun.
On 3rd September 2015, the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) successfully meas... more On 3rd September 2015, the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) successfully measured the linear polarization produced by scattering processes in the hydrogen Lyman-α line of the solar disk radiation, revealing conspicuous spatial variations in the Q/I and U/I signals. Via the Hanle effect the line-center Q/I and U/I amplitudes encode information on the magnetic field of the chromosphere-corona transition region (TR), but they are also sensitive to the three-dimensional structure of this corrugated interface region. With the help of a simple line formation model, here we propose a statistical inference method for interpreting the Lyman-α line-center polarization observed by CLASP.
Construction of the Daniel K. Inouye Solar Telescope (DKIST) is well underway on the Haleakalā su... more Construction of the Daniel K. Inouye Solar Telescope (DKIST) is well underway on the Haleakalā summit on the Hawaiian island of Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration, the DKIST will be the world’s largest solar telescope. It is designed to make high-precision measurements of fundamental astrophysical processes and produce large amounts of spectropolarimetric and imaging data. These data will support research on solar magnetism and its influence on solar wind, flares, coronal mass ejections, and solar irradiance variability. Because of its large aperture, the DKIST will be able to sense the corona’s magnetic field—a goal that has previously eluded scientists—enabling observations that will provide answers about the heating of stellar coronae and the origins of space weather and exo-weather. The telescope will cover a broad wavelength range (0.35 to 28 microns) and operate as a coronagraph at infrared (IR) wavelengths. Achieving the diffraction limit o...
In this chapter we discuss the application of spectro-polarimetry diagnostics to the investigatio... more In this chapter we discuss the application of spectro-polarimetry diagnostics to the investigation of astrophysical plasmas. We first present an overview of why polarization must be expected in the spectral-line radiation that we receive from a large variety of cosmic objects, and then treat in some detail specific atomic models (e.g., the 0–1 and 1–0 two-level atoms), which illustrate how physical and electro-dynamical properties of the emitting plasma can be inferred by studying the polarized radiation in the corresponding spectral lines. The practical applications described in this chapter are taken exclusively from the realm of solar physics, mainly for two reasons: a) From a historical point of view, the Sun was the first cosmic object to which polarization analysis of radiation was successfully applied, proving the existence of solar magnetic fields, and demonstrating the diagnostic potential of radiation phenomena involving resonance polarization. b) Because spectro-polarimet...
We also thank T. Holzer and D. Elmore for helpful comments on an early version of this manuscript... more We also thank T. Holzer and D. Elmore for helpful comments on an early version of this manuscript. Lastly, this work would never have been undertaken without the initial encouragement of A. J. Hundhausen. ix x Judge et al.
Using Government drawings, specifications, or other data included in this document for any purpos... more Using Government drawings, specifications, or other data included in this document for any purpose other than Government procurement does not in any way obligate the U.S. Government. The fact that the Government formulated or supplied the drawings, specifications, or other data does not license the holder or any other person or corporation; or convey any rights or permission to manufacture, use, or sell any patented invention that may relate to them. This report is published in the interest of scientific and technical information exchange and its publication does not constitute the Government’s approval or disapproval of its ideas or findings.
The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) is a sounding rocket experiment designed... more The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) is a sounding rocket experiment designed to measure for the first time the linear polarization of the hydrogen Lyman-α${\alpha}$ line (121.6 nm) and requires a 0.1%$0.1~\%$ polarization sensitivity, which is unprecedented for a spectropolarimeter in the vacuum UV (VUV) spectral range.A unique polarization calibration experiment was conducted under vacuum conditions to estimate the response matrix of the instrument. For this purpose, a custom-made light source was designed to inject Lyman-α${\alpha}$ light with a known linear polarization state into the spectropolarimeter. Two methods were employed to change the orientation of the linear polarization input: one by rotating the light-source itself (direct method), the other by rotating a half-waveplate located after the light-source’s polarizers (waveplate method). The spurious polarization, scale factor, and azimuth error terms of the response matrix were successfully estimated from the polarization calibration measurements. However, it was found that the direct method could not provide an accuracy better than 0.1%$0.1~\%$ on the spurious polarization terms, whereas their required tolerance was <0.017%${<}\,0.017~\%$. On the other hand, the waveplate method determined these terms with only a ∼0.04%${\sim}\,0.04~\%$ accuracy due to residual cross-talk between polarization and intensity. Nevertheless, the polarization calibration confirmed the very low spurious polarization level of the instrument, which will also be confirmed with the flight data. The resulting response matrix deviated from an ideal one, and possible causes of the deviation are discussed by considering the polarization properties of the optical components.
UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts X, 2021
The Polstar mission will provide for a space-borne 60cm telescope operating at UV wavelengths wit... more The Polstar mission will provide for a space-borne 60cm telescope operating at UV wavelengths with spectropolarimetric capability capturing all four Stokes parameters (intensity, two linear polarization components, and circular polarization). Polstar's capabilities are designed to meet its goal of determining how circumstellar gas flows alter massive stars' evolution, and finding the consequences for the stellar remnant population and the stirring and enrichment of the interstellar medium, by addressing four key science objectives. In addition, Polstar will determine drivers for the alignment of the smallest interstellar grains, and probe the dust, magnetic fields, and environments in the hot diffuse interstellar medium, including for the first time a direct measurement of the polarized and energized properties of intergalactic dust. Polstar will also characterize processes that lead to the assembly of exoplanetary systems and that affect exoplanetary atmospheres and habitability. Science driven design requirements include: access to ultraviolet bands: where hot massive stars are brightest and circumstellar opacity is highest; high spectral resolution: accessing diagnostics of circumstellar gas flows and stellar composition in the far-UV at 122-200nm, including the NV, SiIV, and CIV resonance doublets and other transitions such as NIV, AlIII, HeII, and CIII; polarimetry: accessing diagnostics of circumstellar magnetic field shape and strength when combined with high FUV spectral resolution and diagnostics of stellar rotation and distribution of circumstellar gas when combined with low near-UV spectral resolution; sufficient signal-to-noise ratios: ~10 3 for spectropolarimetric precisions of 0.1% per exposure; ~10 2 for detailed spectroscopic studies; ~10 for exploring dimmer sources; and cadence: ranging from 1-10 minutes for most wind variability studies, to hours for sampling rotational phase, to days or weeks for sampling orbital phase. The ISM and exoplanet science program will be enabled by these capabilities driven by the massive star science.
The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provid... more The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provided the first successful measurement of the linear polarization produced by scattering processes in the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In this paper, we report that the Si III line at 120.65nm also shows scattering polarization and we compare the scattering polarization signals observed in the Lyα and Si III lines in order to search for observational signatures of the Hanle effect. We focus on four selected bright structures and investigate how the U/I spatial variations vary between the Lyα wing, the Lyα core, and the Si III line as a function of the total unsigned photospheric magnetic flux estimated from Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations. In an internetwork region, the Lyα core shows an antisymmetric spatial variation across the selected bright structure, but it does not show it in other more magnetized regions. In the Si III line, the spatial variation of U/I deviates from the above-mentioned antisymmetric shape as the total unsigned photospheric magnetic flux increases. A plausible explanation of this difference is the operation of the Hanle effect. We argue that diagnostic techniques based on the scattering polarization observed simultaneously in two spectral lines with very different sensitivities to the Hanle effect, like Lyα and Si III, are of great potential interest for exploring the magnetism of the upper solar chromosphere and transition region.
PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry mission designed to target ... more PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry mission designed to target massive stars and their environments. PolStar will take advantage of resonance lines only available in the FUV to measure for the first time the magnetic and wind environment around massive stars to constrain models of rotation and mass loss.
Proceedings of the International Astronomical Union, 2017
The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new facility led by the High Altitu... more The Coronal Solar Magnetism Observatory (CoSMO) is a proposed new facility led by the High Altitude Observatory and a consortium of partners to measure magnetic field and plasma properties in a large (one degree) field of view extending down to the inner parts of the solar corona. CoSMO is intended as a research facility that will advance the understanding and prediction of space weather. The instrumentation elements of CoSMO are: a white-light coronagraph (KCor), already operational at the Mauna Loa Solar Observatory (MLSO); the Chromosphere and Prominence Magnetometer (ChroMag), due for deployment to MLSO next year; and the CoSMO Large Coronagraph (LC) which has completed Preliminary Design Review.
The Daniel K. Inouye Solar Telescope (DKIST) advances studies of solar magnetism through high-pre... more The Daniel K. Inouye Solar Telescope (DKIST) advances studies of solar magnetism through high-precision and accuracy in polarimetry at frontier spatial and temporal scales. A system model for polarization response in azimuth and altitude has been developed to calibrate DKIST instruments. The DKIST team has developed several new modeling and performance-estimation techniques coupled with thorough metrology. These efforts ensure that quality polarimetry is delivered to meet stringent accuracy requirements. A custom spectropolarimetric calibration system was designed, installed, and used to perform end-to-end calibration of the telescope using the beam within the Cryo-NIRSP instrument. Extensive optical and polarization characterization efforts allow for the reduction of systematic errors within a detailed system model that includes elliptical calibration retarders. Coating witness samples for every relevant optic in the system have been measured. Aperture-dependent variations in polar...
Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospher... more Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospheric physics and sculpting stellar winds. Observations of stellar magnetic fields are typically made in the visible, although infrared observations are becoming common. Here we consider the possibility of directly detecting magnetic fields at ultraviolet (UV) wavelengths using high resolution spectropolarimetry, specifically considering the capabilities of the proposed Polstar mission. UV observations are particularly advantageous for studying wind resonance lines not available in the visible, but they can also provide many photospheric lines in hot stars. Detecting photospheric magnetic fields using the Zeeman effect and Least Squares Deconvolution is potentially more effective in the UV due to the much higher density of strong lines. We investigate detecting magnetic fields in the magnetosphere of a star using the Zeeman effect in wind lines, and find that this could be detectable at high S/N in an O or B star with a strong magnetic field. We consider detecting magnetic fields using the Hanle effect in linear polarization, which is complementary to the Zeeman effect, and could be more sensitive in photospheric lines of rapid rotators. The Hanle effect can also be used to infer circumstellar magnetism in winds. Detecting the Hanle effect requires UV observations, and a multi-line approach is key for inferring magnetic field properties. This demonstrates that high resolution spectropolarimetry in the UV, and the proposed Polstar mission, has the potential to greatly expand our ability to detect and characterize magnetic fields in and around hot stars.
Magnetic fields govern the plasma dynamics in the outer layers of the solar atmosphere, and elect... more Magnetic fields govern the plasma dynamics in the outer layers of the solar atmosphere, and electric fields acting on neutral atoms that move across the magnetic field enable us to study the dynamical coupling between neutrals and ions in the plasma. In order to measure the magnetic and electric fields of chromospheric jets, the full Stokes spectra of the Paschen series of neutral hydrogen in a surge and in some active region jets that took place at the solar limb were observed on May 5, 2012, using the spectropolarimeter of the Domeless Solar Telescope at Hida observatory, Japan. First, we inverted the Stokes spectra taking into account only the effect of magnetic fields on the energy structure and polarization of the hydrogen levels. Having found no definitive evidence of the effects of electric fields in the observed Stokes profiles, we then estimated an upper bound for these fields by calculating the polarization degree under the magnetic field configuration derived in the first step, with the additional presence of a perpendicular (Lorentz type) electric field of varying strength. The inferred direction of the magnetic field on the plane of the sky (POS) approximately aligns to the active region jets and the surge, with magnetic field strengths in the range 10 G < B < 640 G for the surge. Using magnetic field strengths of 70, 200, and 600 G, we obtained upper limits for possible electric fields of 0.04, 0.3, and 0.8 V cm −1 , respectively. This upper bound is conservative, since in our modeling we neglected the possible contribution of collisional depolarization. Because the velocity of neutral atoms of hydrogen moving across the magnetic field derived from these upper limits of the Lorentz electric field is far below the bulk velocity of the plasma perpendicular to the magnetic field as measured by the Doppler shift, we conclude that the neutral atoms must be highly frozen to the magnetic field in the surge.
We present some theoretical predictions concerning the amplitude and magnetic sensitivity of the ... more We present some theoretical predictions concerning the amplitude and magnetic sensitivity of the linear polarization signals produced by scattering processes in the hydrogen Lyα line of the solar transition region. To this end, we have calculated the atomic level polarization (population imbalances and quantum coherences) induced by anisotropic radiation pumping in semi-empirical and hydrodynamical models of the solar atmosphere, taking into account radiative transfer and the Hanle effect caused by the presence of organized and random magnetic fields. The line-center amplitudes of the emergent linear polarization signals are found to vary typically between 0.1% and 1%, depending on the scattering geometry and the strength and orientation of the magnetic field. The results shown here encourage the development of UV polarimeters for sounding rockets and space telescopes with the aim of opening up a diagnostic window for magnetic field measurements in the upper chromosphere and transition region of the Sun.
On 3rd September 2015, the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) successfully meas... more On 3rd September 2015, the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) successfully measured the linear polarization produced by scattering processes in the hydrogen Lyman-α line of the solar disk radiation, revealing conspicuous spatial variations in the Q/I and U/I signals. Via the Hanle effect the line-center Q/I and U/I amplitudes encode information on the magnetic field of the chromosphere-corona transition region (TR), but they are also sensitive to the three-dimensional structure of this corrugated interface region. With the help of a simple line formation model, here we propose a statistical inference method for interpreting the Lyman-α line-center polarization observed by CLASP.
Construction of the Daniel K. Inouye Solar Telescope (DKIST) is well underway on the Haleakalā su... more Construction of the Daniel K. Inouye Solar Telescope (DKIST) is well underway on the Haleakalā summit on the Hawaiian island of Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration, the DKIST will be the world’s largest solar telescope. It is designed to make high-precision measurements of fundamental astrophysical processes and produce large amounts of spectropolarimetric and imaging data. These data will support research on solar magnetism and its influence on solar wind, flares, coronal mass ejections, and solar irradiance variability. Because of its large aperture, the DKIST will be able to sense the corona’s magnetic field—a goal that has previously eluded scientists—enabling observations that will provide answers about the heating of stellar coronae and the origins of space weather and exo-weather. The telescope will cover a broad wavelength range (0.35 to 28 microns) and operate as a coronagraph at infrared (IR) wavelengths. Achieving the diffraction limit o...
In this chapter we discuss the application of spectro-polarimetry diagnostics to the investigatio... more In this chapter we discuss the application of spectro-polarimetry diagnostics to the investigation of astrophysical plasmas. We first present an overview of why polarization must be expected in the spectral-line radiation that we receive from a large variety of cosmic objects, and then treat in some detail specific atomic models (e.g., the 0–1 and 1–0 two-level atoms), which illustrate how physical and electro-dynamical properties of the emitting plasma can be inferred by studying the polarized radiation in the corresponding spectral lines. The practical applications described in this chapter are taken exclusively from the realm of solar physics, mainly for two reasons: a) From a historical point of view, the Sun was the first cosmic object to which polarization analysis of radiation was successfully applied, proving the existence of solar magnetic fields, and demonstrating the diagnostic potential of radiation phenomena involving resonance polarization. b) Because spectro-polarimet...
We also thank T. Holzer and D. Elmore for helpful comments on an early version of this manuscript... more We also thank T. Holzer and D. Elmore for helpful comments on an early version of this manuscript. Lastly, this work would never have been undertaken without the initial encouragement of A. J. Hundhausen. ix x Judge et al.
Using Government drawings, specifications, or other data included in this document for any purpos... more Using Government drawings, specifications, or other data included in this document for any purpose other than Government procurement does not in any way obligate the U.S. Government. The fact that the Government formulated or supplied the drawings, specifications, or other data does not license the holder or any other person or corporation; or convey any rights or permission to manufacture, use, or sell any patented invention that may relate to them. This report is published in the interest of scientific and technical information exchange and its publication does not constitute the Government’s approval or disapproval of its ideas or findings.
The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) is a sounding rocket experiment designed... more The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) is a sounding rocket experiment designed to measure for the first time the linear polarization of the hydrogen Lyman-α${\alpha}$ line (121.6 nm) and requires a 0.1%$0.1~\%$ polarization sensitivity, which is unprecedented for a spectropolarimeter in the vacuum UV (VUV) spectral range.A unique polarization calibration experiment was conducted under vacuum conditions to estimate the response matrix of the instrument. For this purpose, a custom-made light source was designed to inject Lyman-α${\alpha}$ light with a known linear polarization state into the spectropolarimeter. Two methods were employed to change the orientation of the linear polarization input: one by rotating the light-source itself (direct method), the other by rotating a half-waveplate located after the light-source’s polarizers (waveplate method). The spurious polarization, scale factor, and azimuth error terms of the response matrix were successfully estimated from the polarization calibration measurements. However, it was found that the direct method could not provide an accuracy better than 0.1%$0.1~\%$ on the spurious polarization terms, whereas their required tolerance was <0.017%${<}\,0.017~\%$. On the other hand, the waveplate method determined these terms with only a ∼0.04%${\sim}\,0.04~\%$ accuracy due to residual cross-talk between polarization and intensity. Nevertheless, the polarization calibration confirmed the very low spurious polarization level of the instrument, which will also be confirmed with the flight data. The resulting response matrix deviated from an ideal one, and possible causes of the deviation are discussed by considering the polarization properties of the optical components.
UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts X, 2021
The Polstar mission will provide for a space-borne 60cm telescope operating at UV wavelengths wit... more The Polstar mission will provide for a space-borne 60cm telescope operating at UV wavelengths with spectropolarimetric capability capturing all four Stokes parameters (intensity, two linear polarization components, and circular polarization). Polstar's capabilities are designed to meet its goal of determining how circumstellar gas flows alter massive stars' evolution, and finding the consequences for the stellar remnant population and the stirring and enrichment of the interstellar medium, by addressing four key science objectives. In addition, Polstar will determine drivers for the alignment of the smallest interstellar grains, and probe the dust, magnetic fields, and environments in the hot diffuse interstellar medium, including for the first time a direct measurement of the polarized and energized properties of intergalactic dust. Polstar will also characterize processes that lead to the assembly of exoplanetary systems and that affect exoplanetary atmospheres and habitability. Science driven design requirements include: access to ultraviolet bands: where hot massive stars are brightest and circumstellar opacity is highest; high spectral resolution: accessing diagnostics of circumstellar gas flows and stellar composition in the far-UV at 122-200nm, including the NV, SiIV, and CIV resonance doublets and other transitions such as NIV, AlIII, HeII, and CIII; polarimetry: accessing diagnostics of circumstellar magnetic field shape and strength when combined with high FUV spectral resolution and diagnostics of stellar rotation and distribution of circumstellar gas when combined with low near-UV spectral resolution; sufficient signal-to-noise ratios: ~10 3 for spectropolarimetric precisions of 0.1% per exposure; ~10 2 for detailed spectroscopic studies; ~10 for exploring dimmer sources; and cadence: ranging from 1-10 minutes for most wind variability studies, to hours for sampling rotational phase, to days or weeks for sampling orbital phase. The ISM and exoplanet science program will be enabled by these capabilities driven by the massive star science.
The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provid... more The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provided the first successful measurement of the linear polarization produced by scattering processes in the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In this paper, we report that the Si III line at 120.65nm also shows scattering polarization and we compare the scattering polarization signals observed in the Lyα and Si III lines in order to search for observational signatures of the Hanle effect. We focus on four selected bright structures and investigate how the U/I spatial variations vary between the Lyα wing, the Lyα core, and the Si III line as a function of the total unsigned photospheric magnetic flux estimated from Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations. In an internetwork region, the Lyα core shows an antisymmetric spatial variation across the selected bright structure, but it does not show it in other more magnetized regions. In the Si III line, the spatial variation of U/I deviates from the above-mentioned antisymmetric shape as the total unsigned photospheric magnetic flux increases. A plausible explanation of this difference is the operation of the Hanle effect. We argue that diagnostic techniques based on the scattering polarization observed simultaneously in two spectral lines with very different sensitivities to the Hanle effect, like Lyα and Si III, are of great potential interest for exploring the magnetism of the upper solar chromosphere and transition region.
PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry mission designed to target ... more PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry mission designed to target massive stars and their environments. PolStar will take advantage of resonance lines only available in the FUV to measure for the first time the magnetic and wind environment around massive stars to constrain models of rotation and mass loss.
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