W. C. Livingston

INFRARED ATLAS OF THE ARCTURUS SPECTRUM, 0.9-5.3 MICRONS

A spectral atlas of the infrared spectrum of the bright K 2 giant Arcturus has been completed using the 4 meter Mayall telescope and FTS. The 0.9-5.3 micron spectrum of Arcturus was observed at high signal-to-noise with a resolution of 100,000. Telluric lines were removed by using telluric transmission spectra generated from McMath-Pierce solar spectra or 4 meter lunar spectra. The spectrum of Arcturus was observed on two different dates selected to give large opposite heliocentric shifts. The spectra observed on the different dates have been independently corrected for telluric absorption with the result that the telluric spectrum has been effectively removed from all but the most obscure wavelengths of the Arcturus spectrum. We attempted to identify lines with central depths stronger than a few percent. Identifications seem well in hand with the unidentified lines apparantly atmoic in origin. The atlas is available either on an AAS CD-ROM or as an ASP monograph.

Solar magnetograph employing integrated diode arrays

A solar magnetograph employing as detectors a pair of self-scanning 512-element integrated diode arrays is described. Coupled to a 1.5-m telescope, photospheric flux as small as 5(10(16)) maxwells is detected, corresponding in intensity to DeltaI/I = 3(10(-4)) at lambda 0.8688 microm. Measured photometric properties of the diode array are given, including MTF as a function of wavelength, dark current as a function of temperature, completeness of readout, optical and electronic fixed-pattern noise. An integrating preamplifier is presented that achieves a measured noise, when connected to the array, equivalent to 950 electrons at the input for a bandwidth of 3(10(5)) Hz. These data provide a basis for an evaluation of the detector performance at low light levels beyond the needs of the magnetograph. Operated at near liquid nitrogen temperature, the noise and cooling characteristics indicate the detector has promise as a low light level sensor.

Sun-as-a-Star Spectrum Variations 1974-2006

We have observed selected Fraunhofer lines, both integrated over the full disk and for a small circular region near the center of the solar disk, on 1215 days over the past 30 years. Our full disk results for the chromosphere show that Ca II K 3933 A nicely tracks the 11 yr magnetic cycle based on sunspot number, with a peak amplitude in central intensity of ~37%. The wavelength of the midline core absorption feature, called K3, referenced to nearby photospheric Fe, displays an activity cycle variation with an amplitude of 3 mA (6 mA center disk). Other chromospheric lines, such as He I 10830 A, Ca II 8542 A, Hα, and the CN 3883 A bandhead, track Ca II K intensity with lower relative amplitudes. In the low photosphere, temperature-sensitive C I 5380 A appears constant in intensity to 0.2%. In the high photosphere, the cores of strong Fe I lines, Na D1 and D2, and the Mg I b lines, present a puzzling signal, perhaps indicating a role for the 22 yr Hale cycle. Solar minimum around 1985 was clearly seen, but the following minimum in 1996 was missing. Our center disk results show that both Ca II K and C I 5380 A intensities are constant, indicating that the basal quiet atmosphere is unaffected by cycle magnetism within our observational error. A lower limit to the Ca II K central intensity atmosphere is 0.040. This possibly represents conditions as they were during the Maunder minimum. Converted to the Mount Wilson S-index (H+K index), the Sun center disk is at the lower activity limit for solar-type stars. An appendix provides instructions for URL access to both the raw and reduced data.

Magnetograph measurements with temperature-sensitive lines

Certain discrepancies between theoretical and empirical calibrations of magnetograph response are resolved by recognizing the existence of line profile changes in magnetic regions. Many of the photospheric lines commonly used for magnetic field measurements weaken greatly in magnetic regions outside of sunspots. Unless due account is made of the line profile change, the magnetograph measurements underestimate magnetic flux and field strengths.The 5250.2 Å line is especially sensitive to weakening in magnetic regions. Measurements made with this line underestimate the true field by a factor ranging from about two on the linear portion of the profile to five near the line core.

ON A POSSIBLE EXPLANATION OF THE LONG-TERM DECREASE IN SUNSPOT FIELD STRENGTH

Recent studies revealed a controversy in long-term variations in sunspot field strengths. On one hand, the sunspot field strengths computed by averaging both large and small sunspots and pores show a gradual decrease over the declining phase of solar Cycle 23 and the rising phase of Cycle 24. On the other hand, the strongest sunspot field strengths demonstrate only solar cycle variations with no long-term decline. Here, we investigate the field strength and area properties of sunspots in an attempt to reconcile the presence of both tendencies in recent sunspot field strength measurements. First, we analyze the data set from Penn & Livingston, and we show that in addition to the previously reported long-term decline, the data show the solar cycle variation when only sunspots with the strongest magnetic fields are included. Next, we investigate the variations in the number of sunspots of different sizes, and we find a negative correlation between the numbers of small and large sunspots. Finally, we show that during the period of 1998-2011, the number of large sunspots gradually decreased, while the number of small sunspots steadily increased. We suggest that this change in the fraction of small and large sunspots (perhaps, due to changes in the solar dynamo) can explain the gradual decline in average sunspot field strength as observed by Penn & Livingston.

OBSERVATIONAL EVIDENCE FOR QUANTIZATION IN PHOTOSPHERIC MAGNETIC FLUX.

Observations are presented which suggest that away from sunspots photospheric magnetic flux is quantized. Assuming the elemental area of a magnetic region to be 1 (arc-sec)2 the elemental field strength is 525 G.

Kitt Peak 60-cm vacuum telescope

Described is a major new tool for solar research, conceived and built during a time of budget restraint.The observation of magnetic and velocity (circulation) field structure on a synoptic basis and with diffractionlimited resolution is the aim. New optical features include the use of oversize mirrors and windows(to avoid thermal edge effects) and the placement of the coelostat feed outside the vacuum, mainly foreconomy. The site selected has prevailing winds that clear thermals from these mirrors. Test data in theform of the system MTF and optical transmission, together with examples of full disk magnetograms andphotoheliograms, show present performance capability. Measured MTF indicates a response of 0.2 at 1sec of arc (whereas diffraction-limited response would be ~0.8). System transmission, including the accompanying spectrograph, is only 2-3% (lambdaO.44-1.1 microm). Thus, both the optical quality and efficiency aresubject to improvement.

HIGH DISPERSION SPECTROSCOPIC STUDY OF QUIESCENT PROMINENCES.

The utility of very high dispersion spectra (5–11 mm/Å) for the study of line profile and velocity structure in quiescent prominences is demonstrated by observations, taken with the spectregraphic slit positioned normal to the limb in Hα λ6563 Å, He D3 λ5876 Å, and Ca+K λ3933 Å. The emission profiles of both Hα and the K line often show a central reversal (absorption). Emission structures in the K-line can be complex with details as narrow as 0.04 Å. Frequently this structure consists of two distinct components: a central, strong, rather narrow line, and an often displaced, weak feature of undefined profile appearing as ‘fuzz’. It is suggested that this fuzz indicates an exchange of matter between the prominence and the corona.

On the differential rotation with height in the solar atmosphere

Spectroscopic measurements of solar rotation having good height discrimination show no change in angular velocity through the photosphere layers but an increase of 8% for the Hα chromosphere (epoch 1968.9). Spectroscopic results in general are compared with measures made with tracers, i.e. sunspots, filaments, etc., and it is seen that the spectroscopic method always shows increased differential rotation with height, while tracers indicate none. A westward flowing wind is proposed that increases in velocity with height, but produces negligible movement to magnetic regions associated with tracers.

Line-blanketing variations in the irradiance spectrum of the sun from maximum to minimum of the solar cycle

Solar irradiance spectra obtained at or near the maximum and minimum phases of the solar magnetic activity cycle are compared. The characteristics of these spectra are related to the irradiance measurements available from the Active Cavity Radiometer Irradiance Monitor (ACRIM) of the SMM. An interpretation based on sunspots and faculae being added to the atmosphere at solar maximum can account for less than 4 percent of the ACRIM decrease to be arising in the 500-560 nm range. The UV, with its much greater line-blanketing, is more important, in agreement with the finding of Lean (1989). 38 refs.