EARLY CHROMOSPHERIC RESPONSE DURING A SOLAR MICROFLARE OBSERVED WITH SOHO's CDS AND RHESSI

Journal Article · Fri Sep 10 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/720/2/1472· OSTI ID:21460033

Brosius, Jeffrey W ^[1]

---

1. Catholic University of America at NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771 (United States)

We observed a solar microflare with RHESSI and SOHO's Coronal Diagnostic Spectrometer (CDS) on 2009 July 5. With CDS we obtained rapid cadence (7 s) stare spectra within a narrow field of view toward the center of AR 11024. The spectra contain emission lines from ions that cover a wide range of temperature, including He I (<0.025 MK), O V (0.25 MK), Si XII (2 MK), and Fe XIX (8 MK). The start of a precursor burst of He I and O V line emission preceded the steady increase of Fe XIX line emission by about 1 minute and the emergence of 3-12 keV X-ray emission by about 4 minutes. Thus, the onset of the microflare was observed in upper chromospheric (He I) and transition region (O V) line emission before it was detected in high-temperature flare plasma emission. Redshifted O V emission during the precursor suggests explosive chromospheric evaporation, but no corresponding blueshifts were found with either Fe XIX (which was very weak) or Si XII. Similarly, in subsequent microflare brightenings the O V and He I intensities increased (between 49 s and almost 2 minutes) before emissions from the hot flare plasma. Although these time differences likely indicate heating by a nonthermal particle beam, the RHESSI spectra provide no additional evidence for such a beam. In intervals lasting up to about 3 minutes during several bursts, the He I and O V emission line profiles showed secondary, highly blueshifted ({approx}-200 km s{sup -1}) components; during intervals lasting nearly 1 minute the velocities of the primary and secondary components were oppositely directed. Combined with no corresponding blueshifts in either Fe XIX or Si XII, this indicates that explosive chromospheric evaporation occurred predominantly at either comparatively cool temperatures (<2 MK) or within a hot temperature range to which our observations were not sensitive (e.g., between 2 and 8 MK).

• OSTI ID: 21460033
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 720; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
79 ASTRONOMY AND ASTROPHYSICS
ATMOSPHERES
ELECTROMAGNETIC RADIATION
EMISSION
EVAPORATION
GAMMA RADIATION
IONIZING RADIATIONS
MAIN SEQUENCE STARS
MEASURING INSTRUMENTS
PHASE TRANSFORMATIONS
PHOTON EMISSION
PLASMA
RADIATIONS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR CORONA
SOLAR FLARES
SPECTROMETERS
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
STELLAR CORONAE
STELLAR FLARES
SUN
ULTRAVIOLET RADIATION
X RADIATION