2026 March 4 – The seismic diversity of four successive solar cycle minima as observed by the Birmingham Solar-Oscillations Network (BiSON)
We have used data collected by the Birmingham Solar-Oscillations Network (BiSON) to perform a helioseismic diagnosis of changes to the Sun’s internal structure between four successive solar cycle minima, beginning with the minimum at the end of cycle 21 and ending with the recent minimum at the beginning of cycle 25. The unique duration of the BiSON data base makes such a study possible. We used the low-degree BiSON p-mode frequencies to constrain structural changes between minima in the layers above . We accomplished this by examining variations in the He ii ionization zone signature; and by inverting the frequency differences to infer changes in the sound speed. Additionally, we employed frequency differences between various solar models that had subtle modifications to their internal structures to facilitate analysis of the observations. We find evidence for small, but marginally significant, changes in structure between different minima. The He ii signature was larger, and the sound speed in the range to was slightly higher, during the cycle 23/24 minimum, than during the other minima. The cycle 23/24 minimum was the deepest, as measured by proxies of global solar activity. These findings are consistent with magnetic flux levels having been lower in this minimum than the others, resulting in a higher gas pressure, higher temperatures, and higher sound speed. Our results demonstrate the potential of using asteroseismic data to perform similar analyses on other solar-type stars.
@article{10.1093/mnras/stag277,
author = {Basu, Sarbani and Chaplin, William J and Howe, Rachel and Elsworth, Yvonne and Hale, Steven J and Murray, Eleanor},
title = {The seismic diversity of four successive solar cycle minima as observed by the Birmingham Solar-Oscillations Network (BiSON)},
journal = {Monthly Notices of the Royal Astronomical Society},
volume = {547},
number = {1},
pages = {stag277},
year = {2026},
month = {03},
issn = {0035-8711},
doi = {10.1093/mnras/stag277},
url = {https://doi.org/10.1093/mnras/stag277},
eprint = {https://academic.oup.com/mnras/article-pdf/547/1/stag277/66851121/stag277.pdf},
}Download: https://doi.org/10.1093/mnras/stag277
The files contain frequency sets for each cycle minimum period, after weeding.
Columns are: (1) angular degree, l (2) overtone number n (3) frequency (uHz) (4) error (uHz).
@dataset{edata1573,
author = {Basu, Sarbani and Chaplin, William J and Howe, Rachel and Elsworth, Yvonne and Hale, Steven J and Murray, Eleanor},
title = {The seismic diversity of four successive solar cycle minima as observed by the Birmingham Solar-Oscillations Network (BiSON)},
publisher = {Birmingham Solar Oscillations Network},
year = {2026},
month = mar,
doi = {10.25500/edata.bham.00001573},
url = {https://doi.org/10.25500/edata.bham.00001573},
}Download: https://doi.org/10.25500/edata.bham.00001573
2025 January 15 – Far-side helioseismology with Sun-as-a-star data: the solar cycle as seen with 7-d-long BiSON time series
We present results from fitting p-mode spectra derived from 7-d segments of Sun-as-a-star helioseismic observations from the Birmingham Solar Oscillations Network covering 32 yr. The results show a clear dependence of the mode frequencies on solar activity, and the frequency dependence of the sensitivity to activity can also be seen. Because we use data segments that cover less than half of a solar rotation, we are able to test for the effect of activity on the solar far side. By fitting with a model that takes into account activity on the far side of the Sun, we show that the frequency shifts are sensitive to activity from the whole Sun, not just the side facing the observer. Our results suggest that there is potential to investigate activity-related asteroseismic frequency shifts in solar-like oscillators using short time series of observations.
@article{10.1093/mnras/staf090,
author = {Howe, R and Chaplin, W J and Elsworth, Y P and Hale, S J and Hatt, E and Nielsen, M B},
title = {Far-side helioseismology with Sun-as-a-star data: the solar cycle as seen with 7-d-long BiSON time series},
journal = {Monthly Notices of the Royal Astronomical Society},
volume = {537},
number = {2},
pages = {909-914},
year = {2025},
month = {01},
issn = {0035-8711},
doi = {10.1093/mnras/staf090},
url = {https://doi.org/10.1093/mnras/staf090},
eprint = {https://academic.oup.com/mnras/article-pdf/537/2/909/61445281/staf090.pdf},
}Download: https://doi.org/10.1093/mnras/staf090
The file contains mean 7-day frequency shifts (independent shifts only).
Columns are: (1) date (Modified Julian Date, MJD) (2) front-side 10.7-cm Radio Flux (3) far-side 10.7-cm Radio Flux (4) mean frequency shift (uHz) (5) error on mean frequency shift (uHz).
@dataset{edata1572,
author = {Howe, R and Chaplin, W J and Elsworth, Y P and Hale, S J and Hatt, E and Nielsen, M B},
title = {Far-side helioseismology with Sun-as-a-star data: the solar cycle as seen with 7-d-long BiSON time series},
publisher = {Birmingham Solar Oscillations Network},
year = {2025},
month = jan,
doi = {10.25500/edata.bham.00001572},
url = {https://doi.org/10.25500/edata.bham.00001572},
}Download: https://doi.org/10.25500/edata.bham.00001572
2023 September 12 – Low-degree solar rotational splitting from 45 yr of BiSON observations
We present solar low-degree rotational splitting values based on a new analysis of Sun-as-a-star observations from the Birmingham Solar Oscillations Network, covering a 16 425-d period from 1976 December 31 to 2021 December 20 with a duty cycle of 57 per cent. The splitting values are estimated from the power spectrum using a Markov chain Monte Carlo sampling method, and we also present for comparison the results from an analysis of 100 realizations of synthetic data with the same resolution and gap structure. Comparison of the scatter in the results from the synthetic realizations with their estimated uncertainties suggests that for this data set the formal uncertainty estimates are about 30 per cent too small. An upward bias in the splittings at frequencies above 2200 μHz, where the components are not fully resolved, is seen in both the observed and synthetic data. When this bias is taken into account, our results are consistent with a frequency-independent synodic rotational splitting value of 400 nHz.
@article{10.1093/mnras/stad2753,
author = {Howe, Rachel and Chaplin, W J and Elsworth, Y P and Hale, S J and Nielsen, M B},
title = {Low-degree solar rotational splitting from 45 yr of BiSON observations},
journal = {Monthly Notices of the Royal Astronomical Society},
volume = {526},
number = {1},
pages = {1447-1459},
year = {2023},
month = {09},
issn = {0035-8711},
doi = {10.1093/mnras/stad2753},
url = {https://doi.org/10.1093/mnras/stad2753},
eprint = {https://academic.oup.com/mnras/article-pdf/526/1/1447/51791272/stad2753.pdf},
}Download: https://doi.org/10.1093/mnras/stad2753
@dataset{edata1571,
author = {Howe, Rachel and Chaplin, W J and Elsworth, Y P and Hale, S J and Nielsen, M B},
title = {Low-degree solar rotational splitting from 45 yr of BiSON observations},
publisher = {Birmingham Solar Oscillations Network},
year = {2023},
month = sep,
doi = {10.25500/edata.bham.00001571},
url = {https://doi.org/10.25500/edata.bham.00001571},
}Download: https://doi.org/10.25500/edata.bham.00001571
2021 February 11 – Lifetimes and rotation within the solar mean magnetic field
We have used very high-cadence (sub-minute) observations of the solar mean magnetic field (SMMF) from the Birmingham Solar Oscillations Network (BiSON) to investigate the morphology of the SMMF. The observations span a period from 1992 to 2012, and the high-cadence observations allowed the exploration of the power spectrum up to frequencies in the mHz range. The power spectrum contains several broad peaks from a rotationally modulated (RM) component, whose linewidths allowed us to measure, for the first time, the lifetime of the RM source. There is an additional broadband, background component in the power spectrum which we have shown is an artefact of power aliasing due to the low fill of the data. The sidereal rotation period of the RM component was measured as 25.23 ± 0.11 d and suggests that the signal is sensitive to a time-averaged latitude of ∼12°. We have also shown the RM lifetime to be 139.6 ± 18.5 d. This provides evidence to suggest that the RM component of the SMMF is connected to magnetic flux concentrations (MFCs) and active regions (ARs) of magnetic flux, based both on its lifetime and location on the solar disc.
@article{10.1093/mnras/stab405,
author = {Ross, Eddie and Chaplin, William J and Hale, Steven J and Howe, Rachel and Elsworth, Yvonne P and Davies, Guy R and Nielsen, Martin Bo},
title = {Lifetimes and rotation within the solar mean magnetic field},
journal = {Monthly Notices of the Royal Astronomical Society},
volume = {502},
number = {4},
pages = {5603-5611},
year = {2021},
month = {02},
issn = {0035-8711},
doi = {10.1093/mnras/stab405},
url = {https://doi.org/10.1093/mnras/stab405},
eprint = {https://academic.oup.com/mnras/article-pdf/502/4/5603/36455598/stab405.pdf},
}Download: https://doi.org/10.1093/mnras/stab405
@dataset{edata580,
author = {Ross, Eddie and Chaplin, William J and Hale, Steven J and Howe, Rachel and Elsworth, Yvonne P and Davies, Guy R and Nielsen, Martin Bo},
title = {Lifetimes and rotation within the solar mean magnetic field},
publisher = {Birmingham Solar Oscillations Network},
year = {2021},
month = jan,
doi = {10.25500/edata.bham.00000580},
url = {https://doi.org/10.25500/edata.bham.00000580},
}Download: https://doi.org/10.25500/edata.bham.00000580
2020 March 17 – Modelling the response of potassium vapour in resonance scattering spectroscopy
Resonance scattering techniques are often used to study the properties of atoms and molecules. The Birmingham Solar Oscillations Network (BiSON) makes use of Resonance Scattering Spectroscopy by applying the known properties of potassium vapour to achieve ultra-precise Doppler velocity observations of oscillations of the Sun. We present a model of the resonance scattering properties of potassium vapour which can be used to determine the ideal operating vapour temperature and detector parameters within a spectrophotometer. The model is validated against a typical BiSON vapour cell using a tunable diode laser, where the model is fitted to observed absorption profiles at a range of temperatures. Finally we demonstrate using the model to determine the effects of varying scattering detector aperture size, and vapour temperature, and again validate against observed scattering profiles. Such information is essential when designing the next generation of BiSON spectrophotometers (BiSON:NG), where the aim is to make use of off-the-shelf components to simplify and miniaturise the instrumentation as much as practical.
@article{Hale_2020,
doi = {10.1088/1361-6455/ab7529},
url = {https://doi.org/10.1088/1361-6455/ab7529},
year = {2020},
month = {mar},
publisher = {IOP Publishing},
volume = {53},
number = {8},
pages = {085003},
author = {Hale, S J and Chaplin, W J and Davies, G R and Elsworth, Y P},
title = {Modelling the response of potassium vapour in resonance scattering spectroscopy},
journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}
}Download: https://doi.org/10.1088/1361-6455/ab7529
@dataset{edata417,
author = {Hale, S J and Chaplin, W J and Davies, G R and Elsworth, Y P},
title = {Modelling the response of potassium vapour in resonance scattering spectroscopy},
publisher = {Birmingham Solar Oscillations Network},
year = {2020},
month = jan,
doi = {10.25500/edata.bham.00000417},
url = {https://doi.org/10.25500/edata.bham.00000417},
}Download: https://doi.org/10.25500/edata.bham.00000417
2020 January 28 – Measurement of Atmospheric Scintillation during a Period of Saharan Dust (Calima) at Observatorio del Teide, Izana, Tenerife, and the Impact on Photometric Exposure Times
We present scintillation noise profiles captured at the Observatorio del Teide, Izaña, Tenerife, over a one-week period in 2017 September. Contemporaneous data from the Birmingham Solar Oscillations Network (BiSON) and the Stellar Activity (STELLA) robotic telescopes provides estimates of daily atmospheric extinction allowing the scintillation noise to be placed within the context of overall atmospheric conditions. We discuss the results both in terms of the impact on BiSON spectrophotometer design, and for astronomical observations more generally. We find that scintillation noise power reduces by half at about 5 Hz, and is reduced to one tenth between 20 and 30 Hz even during periods of mild Calima, where visibility is reduced due to high concentrations of mineral dust in the atmosphere. We show that the common accepted exposure time of <10 ms for limiting the effect of scintillation noise in ground based photometry may be increased, and that depending on the application there may be little benefit to achieving exposure times shorter than 50 ms, relaxing constraints on detector gain and bandwidth.
@article{Hale_2020,
doi = {10.1088/1538-3873/ab6753},
url = {https://doi.org/10.1088/1538-3873/ab6753},
year = {2020},
month = {jan},
publisher = {The Astronomical Society of the Pacific},
volume = {132},
number = {1009},
pages = {034501},
author = {Hale, S. J. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. P. and Howe, R. and Pallé, P. L.},
title = {Measurement of Atmospheric Scintillation during a Period of Saharan Dust (Calima) at Observatorio del Teide, Iz̃ana, Tenerife, and the Impact on Photometric Exposure Times},
journal = {Publications of the Astronomical Society of the Pacific}
}Download: https://doi.org/10.1088/1538-3873/ab6753
@dataset{edata412,
author = {Hale, S. J. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. P. and Howe, R. and Pallé, P. L.},
title = {Measurement of Atmospheric Scintillation during a Period of Saharan Dust (Calima) at Observatorio del Teide, Iz̃ana, Tenerife, and the Impact on Photometric Exposure Times},
publisher = {Birmingham Solar Oscillations Network},
year = {2019},
month = dec,
doi = {10.25500/edata.bham.00000412},
url = {https://doi.org/10.25500/edata.bham.00000412},
}Download: https://doi.org/10.25500/edata.bham.00000412
2017 August 11 – Atmospheric Extinction Coefficients in the Ic Band for Several Major International Observatories: Results from the BiSON Telescopes, 1984–2016
Over 30 years of solar data have been acquired by the Birmingham Solar Oscillations Network (BiSON), an international network of telescopes used to study oscillations of the Sun. Five of the six BiSON telescopes are located at major observatories. The observational sites are, in order of increasing longitude: Mount Wilson (Hale) Observatory (MWO), California, USA; Las Campanas Observatory, Chile; Observatorio del Teide, Izaña, Tenerife, Canary Islands; the South African Astronomical Observatory, Sutherland, South Africa; Carnarvon, Western Australia; and the Paul Wild Observatory, Narrabri, New South Wales, Australia. The BiSON data may be used to measure atmospheric extinction coefficients in the band (approximately 700–900 nm), and presented here are the derived atmospheric extinction coefficients from each site over the years 1984–2016.
@article{Hale_2017,
doi = {10.3847/1538-3881/aa81d0},
url = {https://doi.org/10.3847/1538-3881/aa81d0},
year = {2017},
month = {aug},
publisher = {The American Astronomical Society},
volume = {154},
number = {3},
pages = {89},
author = {Hale, S. J. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. P. and Howe, R. and Lund, M. N. and Moxon, E. Z. and Thomas, A. and Pallé, P. L. and Rhodes, E. J.},
title = {Atmospheric Extinction Coefficients in the Ic Band for Several Major International Observatories: Results from the BiSON Telescopes, 1984–2016},
journal = {The Astronomical Journal}
}Download: https://doi.org/10.3847/1538-3881/aa81d0
@dataset{edata25,
author = {Hale, S. J. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. P. and Howe, R. and Lund, M. N. and Moxon, E. Z. and Thomas, A. and Pallé, P. L. and Rhodes, E. J.},
title = {Atmospheric Extinction Coefficients in the Ic Band for Several Major International Observatories: Results from the BiSON Telescopes, 1984–2016},
publisher = {Birmingham Solar Oscillations Network},
year = {2017},
month = jul,
doi = {10.25500/edata.bham.00000025},
url = {https://doi.org/10.25500/edata.bham.00000025},
}Download: https://doi.org/10.25500/eData.bham.00000025
2015 December 7 – Performance of the Birmingham Solar-Oscillations Network (BiSON)
The Birmingham Solar-Oscillations Network (BiSON) has been operating with a full complement of six stations since 1992. Over 20 years later, we look back on the network history. The meta-data from the sites have been analysed to assess performance in terms of site insolation, with a brief look at the challenges that have been encountered over the years. We explain how the international community can gain easy access to the ever-growing dataset produced by the network, and finally look to the future of the network and the potential impact of nearly 25 years of technology miniaturisation.
@article{Hale2016,
author="Hale, S. J. and Howe, R. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. P.",
title="Performance of the Birmingham Solar-Oscillations Network (BiSON)",
journal="Solar Physics",
year="2016",
month="Jan",
day="01",
volume="291",
number="1",
pages="1--28",
issn="1573-093X",
doi="10.1007/s11207-015-0810-0",
url="https://doi.org/10.1007/s11207-015-0810-0"
}Download: https://doi.org/10.1007/s11207-015-0810-0
@dataset{edata59,
title = {{BiSON - All Sites - 1995 to 2014 - Performance Check}},
author = {Hale, S. J.},
publisher = {Birmingham Solar Oscillations Network},
year = {2015},
month = may,
doi = {10.25500/eData.bham.00000059},
url = {https://doi.org/10.25500/eData.bham.00000059},
}Download: https://doi.org/10.25500/eData.bham.00000059
2014 February 7 – Low-frequency, low-degree solar p-mode properties from 22 years of Birmingham Solar Oscillations Network data
The solar low-degree low-frequency modes of oscillation are of particular interest as their frequencies can be measured with very high precision and hence provide good constraints on seismic models. Here we detect and characterize these valuable measures of the solar interior from a 22 yr Birmingham Solar Oscillations Network data set. We report mode frequencies, line widths, heights, amplitudes, and rotational splitting, all with robust uncertainties. The new values of frequency, rotational splitting, amplitude, and line width we provide will help place new constraints on hydrostatic and rotational structure, plus diagnostics of near-surface convection. Further to this, by assuming simple power laws, we extrapolate mode properties to lower frequencies. We demonstrate that the low-l low-frequency p modes have a low signal-to-noise ratio and that this cannot be overcome simply by continued observation. It will be necessary to observe the Sun in novel ways to ‘beat’ the intrinsic granulation noise.
@article{10.1093/mnras/stu080,
author = {Davies, G. R. and Broomhall, A. M. and Chaplin, W. J. and Elsworth, Y. and Hale, S. J.},
title = {Low-frequency, low-degree solar p-mode properties from 22 years of Birmingham Solar Oscillations Network data},
journal = {Monthly Notices of the Royal Astronomical Society},
volume = {439},
number = {2},
pages = {2025-2032},
year = {2014},
month = {02},
issn = {0035-8711},
doi = {10.1093/mnras/stu080},
url = {https://doi.org/10.1093/mnras/stu080},
eprint = {https://academic.oup.com/mnras/article-pdf/439/2/2025/18472646/stu080.pdf},
}Download: https://doi.org/10.1093/mnras/stu080
@dataset{edata1570,
author = {Davies, G. R. and Broomhall, A. M. and Chaplin, W. J. and Elsworth, Y. and Hale, S. J.},
title = {Low-frequency, low-degree solar p-mode properties from 22 years of Birmingham Solar Oscillations Network data},
publisher = {Birmingham Solar Oscillations Network},
year = {2014},
month = feb,
doi = {10.25500/edata.bham.00001570},
url = {https://doi.org/10.25500/edata.bham.00001570},
}Download: https://doi.org/10.25500/edata.bham.00001570
2009 June 1 – Definitive Sun-as-a-star p-mode frequencies: 23 years of BiSON observations
We present a list of ‘best possible’ estimates of low-degree p-mode frequencies from 8640 days of observations made by the Birmingham Solar-Oscillations Network (BiSON). This is the longest stretch of helioseismic data ever used for this purpose, giving exquisite precision in the estimated frequencies. Every effort has been made in the analysis to ensure that the frequency estimates are also accurate. In addition to presenting the raw best-fitting frequencies from our ‘peak-bagging’ analysis, we also provide tables of corrected frequencies pertinent to the quiet-Sun and an intermediate level of solar activity.
@article{10.1111/j.1745-3933.2009.00672.x,
author = {Broomhall, A.-M. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. and Fletcher, S. T. and Hale, S. J. and Miller, B. and New, R.},
title = {Definitive Sun-as-a-star p-mode frequencies: 23 years of BiSON observations},
journal = {Monthly Notices of the Royal Astronomical Society: Letters},
volume = {396},
number = {1},
pages = {L100-L104},
year = {2009},
month = {06},
issn = {1745-3925},
doi = {10.1111/j.1745-3933.2009.00672.x},
url = {https://doi.org/10.1111/j.1745-3933.2009.00672.x},
eprint = {https://academic.oup.com/mnrasl/article-pdf/396/1/L100/54679126/mnrasl_396_1_l100.pdf},
}Download: https://doi.org/10.1111/j.1745-3933.2009.00672.x
@dataset{edata1569,
author = {Broomhall, A.-M. and Chaplin, W. J. and Davies, G. R. and Elsworth, Y. and Fletcher, S. T. and Hale, S. J. and Miller, B. and New, R.},
title = {Definitive Sun-as-a-star p-mode frequencies: 23 years of BiSON observations},
publisher = {Birmingham Solar Oscillations Network},
year = {2009},
month = jun,
doi = {10.25500/edata.bham.00001569},
url = {https://doi.org/10.25500/edata.bham.00001569},
}