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Indications of stellar coronal mass ejections through coronal dimmings

Abstract

Coronal mass ejections (CMEs) are huge expulsions of magnetized matter from the Sun and stars, traversing space with speeds of millions of kilometres per hour. Solar CMEs can cause severe space weather disturbances and consumer power outages on Earth, whereas stellar CMEs may even pose a hazard to the habitability of exoplanets. Although CMEs ejected by our Sun can be directly imaged by white-light coronagraphs, for stars this is not possible. So far, only a few candidates for stellar CME detections have been reported. Here we demonstrate a different approach that is based on sudden dimmings in the extreme ultraviolet and X-ray emission caused by the CME mass loss. We report dimming detections associated with flares on cool stars, indicative of stellar CMEs, and which are benchmarked by Sun-as-a-star extreme ultraviolet measurements. This study paves the way for comprehensive detections and characterizations of CMEs on stars, which are important factors in planetary habitability and stellar evolution.

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Fig. 1: Coronal dimming event on Sun on 2012 March 7.
Fig. 2: Coronal dimmings on Proxima Centauri.
Fig. 3: Coronal dimming on AB Dor.
Fig. 4: Characteristics of solar and stellar dimmings.

Data availability

The solar data used in this study are publicly available from the SDO–EVE data archive (http://lasp.colorado.edu/eve/data_access/eve_data/products/level2/) and the SDO–AIA data archive (http://jsoc.stanford.edu/ajax/lookdata.html?ds=aia.lev1_euv_12s). The stellar data used in this study are publicly available at the XMM-Newton Science Archive (http://nxsa.esac.esa.int/nxsa-web/#search), the Chandra Data Archive (https://cda.harvard.edu/chaser/) and the EUVE data archive at the Mikulski Archive for Space Telescopes (https://archive.stsci.edu/euve/search.php). The specific stellar datasets used in this study are uniquely identified by their archive’s Observation ID given in Supplementary Table 2. The resulting solar and stellar dimming parameters are given in Supplementary Tables 1 and 2.

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Acknowledgements

We have made use of data obtained through the XMM-Newton Science Data Archive, operated by ESA at VILSPA, the Chandra Data Archive, operated by the Smithsonian Astrophysical Observatory for NASA, and the Mikulski Archive for Space Telescope for EUVE operated by the Space Telescope Science Institute. SDO data are courtesy of NASA–SDO and the AIA and EVE science teams. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. We thank the members of the International Space Science institute (ISSI) team on ‘Coronal Dimmings and their Relevance to the Physics of Solar and Stellar Coronal Mass Ejections' for fruitful discussions. We thank J. Sanz-Forcada for help in the reduction of EUVE data. A.M.V., P.O., M.L., K.D. and N.C.F. acknowledge the Austrian Space Applications Programme of the Austrian Research Promotion Agency FFG (ASAP-14 865972, BMVIT). M.L. and P.O. acknowledge the Austrian Science Fund (FWF), P30949-N36.

Author information

Affiliations

Authors

Contributions

A.M.V. conceptualized and led the study, co-designed its solar part and led the writing. P.O. co-designed the stellar part of the study and analysed the XMM-Newton data. M.L. co-designed the stellar part of the study and analysed the Chandra and EUVE data. K.D. co-designed the solar part of the study and analysed the SDO–AIA data. N.C.F. analysed the SDO–EVE data. H.S.H. contributed to the SDO–EVE spectral analysis. All authors discussed the results and contributed to the manuscript text.

Corresponding author

Correspondence to Astrid M. Veronig.

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Competing interests

The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Eric Houdebine and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Selected examples illustrating the manifold of coronal dimming appearances for CME-associated solar flares.

Top subpanels: GOES full-Sun 0.1–0.8 nm soft X-ray flux, dominated by the hot flare emission. Bottom subpanels: SDO/EVE full-Sun 15–25 nm light curves showing the flares and coronal dimmings. The red line shows the weighted cubic spline fit. Green data points are used for calculation of pre-flare level. Horizontal lines represent the pre-flare (solid) and corresponding 2𝜎 (dashed) level used to identify significant dimming emission decreases. Vertical lines indicate the times of the dimming start, maximum depth and end.

Extended Data Fig. 2 Selected examples of light curves for confined solar flares.

a) A confined flare (GOES class M4.9) which shows no dimming (true negative), b) the only confined flare (GOES class M6.3) where a significant EVE dimming was identified (false positive). Note that starting around 05:00 UT on 2 Nov 2013 there is a pronounced dimming associated with an eruptive C8.2 flare. Same plot format as Extended Data Fig. 1.

Extended Data Fig. 3 Background subtracted X-ray light curves of the fast-rotating K-type star AB Dor.

Data from the XMM EPIC PN (left and right columns) and MOS1 (middle column) detectors are shown as filled symbols, and are plotted for the total energy band (0.2–12 keV) as well as four subbands. Bin sizes of 100s, 200s, and 100s were used (from left to right). The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The time is given in hours relative to the start of the PN or MOS1 exposures. The right y-axes give the relative differences in per cent between the quiet levels and the data. The upper x-axes show the stellar rotation phase, starting from the beginning of the observations. Error bars are the errors returned by the epiclccorr task. Small dark gray symbols visible in some panels indicate the background light curve in the same energy band. No simultaneous photometric observations are available for the event shown in the left column. For the other two events, simultaneous photometric fast mode observations in the UVW2 (middle) and UVM2 (right) bands are shown in the lowest panels. The fast mode data were rebinned to 200s. Bin widths are indicated by the horizontal bars, count rate errors were determined by standard error propagation of the errors returned by the omfchain task for the standard 10s binning. The dimming event in the middle column is only significant with the optimized binning method.

Extended Data Fig. 4 Background subtracted X-ray light curves of the fast-rotating K-type stars AB Dor (left column), CD-53 544 (middle column) and LO Peg (right column).

Data from the XMM EPIC PN detector are shown as filled symbols, and are plotted for the total energy band (0.2–12 keV) as well as four subbands. Bin sizes of 100s, 300s, and 100s were used (from left to right). The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The time is given in hours relative to the start of the PN exposures. The right y-axes give the relative differences in per cent between the quiet levels and the data. The upper x-axes show the stellar rotation phases, starting from the beginning of the observations. Error bars are the errors returned by the epiclccorr task. Small dark gray symbols visible in some panels indicate the background light curve in the same energy band. Simultaneous photometric imaging mode observations in the UVW2 bands (left), as well as fast mode observations in the UVW1 (middle; data in other bands before and after the event are omitted due to their different flux level) and UVM2 (right) bands are shown in the lowest panels. The fast mode data were rebinned to 400s. In the left column, exposure times are indicated by the horizontal bars, magnitude errors are the errors returned by the omichain task. In the other columns, bin widths are indicated by the horizontal bars, count rate errors were determined by standard error propagation of the errors returned by the omfchain task for the standard 10s binning.

Extended Data Fig. 5 Background subtracted X-ray light curves of the G-type stars 47 Cas B (left column), EK Dra (middle column) and VB 50 (right column).

Data from the XMM EPIC PN detector are shown as filled symbols, and are plotted for the total energy band (0.2–12 keV) as well as four subbands. Bin sizes of 400s, 300s, and 400s were used (from left to right). The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The time is given in hours relative to the start of the PN exposures. The right y-axes give the relative differences in percent between the quiet levels and the data. Error bars are the errors returned by the epiclccorr task. Small dark gray symbols visible in some panels indicate the background light curve in the same energy band. No simultaneous photometric observations are available for 47 Cas B and VB 50. For EK Dra, simultaneous photometric imaging mode observations in the UVW2 band are shown in the lowest panel. Exposure times are indicated by the horizontal bars, magnitude errors are the errors returned by the omichain task. The dimming event of EK Dra is only significant (maximum dimming depth >2σ%) with the optimized binning method.

Extended Data Fig. 6 Background subtracted X-ray light curves of the young M-type star AU Mic.

Data from the XMM EPIC PN detector are shown as filled symbols, and are plotted for the total energy band (0.2–12 keV) as well as four subbands. Bin sizes of 300s were used. The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The time is given in hours relative to the start of the PN exposures. The right y-axes give the relative differences in per cent between the quiet levels and the data. Error bars are the errors returned by the epiclccorr task. Small dark gray symbols visible in some panels indicate the background light curve in the same energy band. Simultaneous photometric fast mode observations for the event shown in the right column are omitted, as they are corrupted after the first 7 hours of the observation. For the other two events, simultaneous photometric fast mode observations in the UVW2 band are shown in the lowest panels. The fast mode data were rebinned to 300s. Bin widths are indicated by the horizontal bars, count rate errors were determined by standard error propagation of the errors returned by the omfchain task for the standard 10s binning.

Extended Data Fig. 7 Background subtracted X-ray light curves of the M-type stars CN Leo (left column), GJ 669 AB (middle column) and GSC 07396–00759 (right column).

Data from the XMM EPIC PN detector are shown as filled symbols, and are plotted for the total energy band (0.2–12 keV) as well as four subbands. Bin sizes of 100s, 200s, and 1000s were used (from left to right). The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The time is given in hours relative to the start of the PN exposures. The right y-axes give the relative differences in per cent between the quiet levels and the data. Error bars are the errors returned by the epiclccorr task. Small dark gray symbols visible in some panels indicate the background light curve in the same energy band. For GJ 669 AB, the available imaging photometry consists of one image in each filter band, which cannot be used to create a photometric light curve. For CN Leo, they were omitted, as the fast mode observations are corrupted and the imaging mode observations have a too low cadence. For GSC 07396–00759, the imaging mode observations are also omitted because of their too low cadence. Moreover, the last few hours of this observation (time>30h) are affected by a strong background flare, making the data in the highest energy bin (lowest panel) unusable. The dimming events of CN Leo and GJ 669 AB are only significant with the optimized binning method.

Extended Data Fig. 8 Background subtracted X-ray light curves of Proxima Cen.

Data from the XMM EPIC PN (left) and MOS1 (right) detectors are shown as filled symbols, and are plotted for the energy band 0.2–2 keV as well as four subbands (in both cases, data from 2–12 keV are not usable). Bin sizes of 200s and 400s were used (from left to right). The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The time is given in hours relative to the start of the PN or MOS1 exposures. The right y-axes give the relative differences in per cent between the quiet levels and the data. Error bars are the errors returned by the epiclccorr task. Small dark gray symbols visible in some panels indicate the background light curve in the same energy band. Simultaneous photometric fast mode observations in the U band are shown in the lowest panels. The fast mode data were rebinned to 100s (left) and 300s (right). Bin widths are indicated by the horizontal bars, count rate errors were determined by standard error propagation of the errors returned by the omfchain task for the standard 10s binning.

Extended Data Fig. 9 Chandra ACIS HETGS light curves of the rapidly rotating young star PZ Tel (left panels) and the young binary star EQ Peg (right panels).

The data are plotted for the total energy band (0.4–12 keV) as well as three subbands. All light curves are binned to 500s. The weighted spline fits to the data are shown as blue lines, the adopted quiet levels as red dashed lines. The quiet time intervals are indicated as gray shaded areas, the detected dimming regions as blue shaded areas (dark blue: maximum dimming depth >2σ%, light blue: maximum dimming depth <2σ%). The right y-axes give the relative differences in per cent between the quiet levels and the data. The upper x-axes show the stellar rotation phases, starting from the beginning of the observations. Error bars are the errors returned by the aglc task. The first dimming event of PZ Tel is only significant with the optimized binning method.

Extended Data Fig. 10 Background subtracted X-ray (0.2–12 keV) light curves of Proxima Cen.

This plot includes all eight available XMM observations with EPIC data, spanning the years from 2001 to 2018. Here we use the MOS1 exposures, because of their slightly longer durations than the PN exposures of the same observations. The dimming events are included in the last two observations. Error bars are omitted here for clarity. This representation shows that the dimming events are associated with small short flares, which can be understood in terms of better observability of the dimming compared to the bright flare emission.

Supplementary information

Supplementary Information

Supplementary information on the stars where stellar dimmings were identified, Video 1 and Tables 1 and 2.

Supplementary Video 1

Coronal dimming event on Sun on 2012 March 7. In the top panels, the video shows the time evolution of the event in SDO–AIA 19.3 nm direct (left) and logarithmic base-ratio (middle) images, and the spatially resolved SDO–AIA 19.3 nm light curves (right) of the flare and dimming regions. The bottom panels show the evolution of the SDO/EVE pre-event subtracted SDO–EVE irradiance spectra (left; red colour highlights increases, blue colour highlights decreases in the spectral emission) and the SDO–EVE 15–25 nm Sun-as-a-Star light curve (right). The vertical bars in the plotted times series indicate the time corresponding to the imaging and spectral evolution shown to the left.

Supplementary Table 1

Solar dimmings. The dimmings are identified in full-Sun SDO–EVE 15–25 nm and SDO–AIA 19.3 nm light curves. Column 1 gives the date and start of the flare, column 2 the GOES soft X-ray flare class and column 3 the heliographic position of the flare. Column 4 states whether there was a CME associated with the flare. Columns 5 and 6 state whether a significant dimming was identified in the SDO–EVE 15–25 nm and AIA 19.3 nm light curves, respectively. Columns 7–11 give the derived SDO–EVE 15–25 nm dimming parameters: maximum depth and corresponding significance (𝜎), duration (tdim), rise time (trise) and recovery time (trec). Columns 12 and 13 list the time between flare peak and dimming maximum (tfp_dm) and the time between flare peak and dimming start (tfp_ds), respectively.

Supplementary Table 2

Stellar dimmings. The first four columns give the characteristics of the star on which the dimming occurred (name, spectral type from SIMBAD100, rotation period, age). In column 1, we also specify the corresponding plots shown in the Extended Data (indicated by an ‘E’ before the figure number) and the main text. Column 5 gives the unique observation IDs of the used datasets for each mission (column 6), as well as the start dates and times of the observations. Columns 7–12 give the derived dimming parameters: maximum depth and corresponding significance (𝜎), start time (tstart) of dimming relative to the start of the observation, duration (tdim), rise time from dimming start to maximum (trise) and recovery time (trec). Columns 13 and 14 give the time between flare peak and dimming maximum (tfp_dm) and the time between flare peak and dimming start (tfp_ds), respectively. Note that not all dimming depths listed in column 7 are >2𝜎%, because the given values refer to the total energy band, but some dimmings are only significant in smaller subbands. The total energy bands are 0.2–12 keV for XMM-Newton (except for Proxima Cen, where only 0.2–2 keV were usable), 0.4–12 keV for Chandra and 0.07–0.15 keV for EUVE.

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Veronig, A.M., Odert, P., Leitzinger, M. et al. Indications of stellar coronal mass ejections through coronal dimmings. Nat Astron (2021). https://doi.org/10.1038/s41550-021-01345-9

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