Detection and Astrometry of the Ba-Bb Subsystem in $α$ Piscium: First Dual-Field Interferometry at the CHARA Array
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2026
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| author | Anugu, Narsireddy Klement, Robert Monnier, John D. Gies, Douglas R. Schaefer, Gail H. Kraus, Stefan Carrazco-Gaxiola, Sebastián Chaturvedi, Akshat S. Gutierrez, Mayra Flores, Becky Jones, Jeremy Kane, Colin Köhler, Rainer Kubiak, Karolina Majoinen, Olli W. Scott, Nicholas J. Sharifi, Kayvon |
| author_facet | Anugu, Narsireddy Klement, Robert Monnier, John D. Gies, Douglas R. Schaefer, Gail H. Kraus, Stefan Carrazco-Gaxiola, Sebastián Chaturvedi, Akshat S. Gutierrez, Mayra Flores, Becky Jones, Jeremy Kane, Colin Köhler, Rainer Kubiak, Karolina Majoinen, Olli W. Scott, Nicholas J. Sharifi, Kayvon |
| contents | We present the first on-sky demonstration of dual-field interferometry at the CHARA Array and the first direct resolution of the inner Ba--Bb subsystem in the bright hierarchical triple $α$ Piscium. Using $H$-band fringe tracking on component A with MIRC-X to stabilize $K$-band science fringes on component B with MYSTIC, we detected a companion at a projected separation of 7 mas, confirming a long-suspected but previously unresolved short-period subsystem within the B component. The nearly equal $H/K$-band flux ratio indicates that Ba and Bb are near-twin F-type stars, consistent with the two narrow-lined components seen in optical spectra of B. By combining CHARA interferometry with archival VLTI/GRAVITY astrometry and radial velocities from archival and new spectroscopy (NARVAL and ARCES), we derive a well-constrained orbit with a period of $P = 25$ d, eccentricity $e \simeq 0.6$, and inclination $i \simeq 65^\circ$, yielding precise dynamical masses of $1.668\pm0.033\,M_\odot$ and $1.646\pm0.029\,M_\odot$. No additional companion is detected down to $ΔH \approx 5$ at separations of 0.2--2 AU. We also obtained dual-field differential astrometry of the wide A--B pair with a precision of ~0.234 mas at a separation of $1.85''$, with an error budget dominated by internal delay-line actuators, fringe-tracking performance and chromatic dispersion. While the long-period outer orbit is not refined by these measurements, their agreement with the published astrometric orbit provides an on-sky validation of the CHARA dual-field mode. These results establish $α$ Psc as a well-characterized hierarchical system suitable for future benchmark studies and demonstrate CHARA's new capability for off-axis interferometry and sub-mas astrometry on arcsecond-scale binaries. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_09489 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Detection and Astrometry of the Ba-Bb Subsystem in $α$ Piscium: First Dual-Field Interferometry at the CHARA Array Anugu, Narsireddy Klement, Robert Monnier, John D. Gies, Douglas R. Schaefer, Gail H. Kraus, Stefan Carrazco-Gaxiola, Sebastián Chaturvedi, Akshat S. Gutierrez, Mayra Flores, Becky Jones, Jeremy Kane, Colin Köhler, Rainer Kubiak, Karolina Majoinen, Olli W. Scott, Nicholas J. Sharifi, Kayvon Solar and Stellar Astrophysics Instrumentation and Methods for Astrophysics We present the first on-sky demonstration of dual-field interferometry at the CHARA Array and the first direct resolution of the inner Ba--Bb subsystem in the bright hierarchical triple $α$ Piscium. Using $H$-band fringe tracking on component A with MIRC-X to stabilize $K$-band science fringes on component B with MYSTIC, we detected a companion at a projected separation of 7 mas, confirming a long-suspected but previously unresolved short-period subsystem within the B component. The nearly equal $H/K$-band flux ratio indicates that Ba and Bb are near-twin F-type stars, consistent with the two narrow-lined components seen in optical spectra of B. By combining CHARA interferometry with archival VLTI/GRAVITY astrometry and radial velocities from archival and new spectroscopy (NARVAL and ARCES), we derive a well-constrained orbit with a period of $P = 25$ d, eccentricity $e \simeq 0.6$, and inclination $i \simeq 65^\circ$, yielding precise dynamical masses of $1.668\pm0.033\,M_\odot$ and $1.646\pm0.029\,M_\odot$. No additional companion is detected down to $ΔH \approx 5$ at separations of 0.2--2 AU. We also obtained dual-field differential astrometry of the wide A--B pair with a precision of ~0.234 mas at a separation of $1.85''$, with an error budget dominated by internal delay-line actuators, fringe-tracking performance and chromatic dispersion. While the long-period outer orbit is not refined by these measurements, their agreement with the published astrometric orbit provides an on-sky validation of the CHARA dual-field mode. These results establish $α$ Psc as a well-characterized hierarchical system suitable for future benchmark studies and demonstrate CHARA's new capability for off-axis interferometry and sub-mas astrometry on arcsecond-scale binaries. |
| title | Detection and Astrometry of the Ba-Bb Subsystem in $α$ Piscium: First Dual-Field Interferometry at the CHARA Array |
| topic | Solar and Stellar Astrophysics Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2603.09489 |