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In this review presented at the Symposium A stellar journey in Uppsala, June 2008, I give my account of the historical development of the MARCS code from the first version published in 1975 and its premises to the 2008 grid. It is shown that the primary driver for the development team is the science that can be done with the models, and that they constantly strive to include the best possible physical data. A few preliminary comparisons of M star model spectra to spectrophotometric observations are presented. Particular results related to opacity effects are discussed. The size of errors in the spectral energy distribution (SED) and model thermal stratification are estimated for different densities of the wavelength sampling. The number of points used in the MARCS 2008 grid (108000) is large enough to ensure errors of only a few K in all models of the grid, except the optically very thin layers of metal-poor stars. Errors in SEDs may reach about 10% locally in the UV. The published sampled SEDs are thus appropriate to compute synthetic broad-band photometry, but higher resolution spectra will be computed in the near future and published as well on the MARCS site (marcs.astro.uu.se). Test model calculations with TiO line opacity accounted for in scattering show an important cooling of the upper atmospheric layers of red giants. Rough estimates of radiative and collisional time scales for electronic transitions of TiO indicate that scattering may well be the dominant mechanism in these lines. However models constructed with this hypothesis are incompatible with optical observations of TiO (Arcturus) or IR observations of OH (Betelgeuse), although they may succeed in explaining H2O line observations. More work is needed in that direction., Review talk at the conference "A stellar journey" held in Uppsala, June 2008. In press in Physica Scripta, eds. Paul Barklem, Andreas Korn, and Bertrand Plez

Spectra of the 4.7 um bands of carbon monoxide in absorption, and spectra of the cores of the 0.4 um resonance lines of ionized calcium in emission, might be used to diagnose the presence of atmospheric inhomogeneities, caused by the action of surface magnetic fields, on stars as diverse as the Sun and the red giant Arcturus.

A mixing length model of the convection zone of Arcturus is used to study the influence of varying physical parameters on the turbulent sound generation mechanism. It is found that the chemical composition determines the structure of the convection zone. The periods and wavelengths of the generated waves are much larger than for the sun.

By observing the p-mode oscillation spectrum of a star and determining its first and second order frequency spacings, Δv and δ, it is possible to obtain constraints which are useful in modeling the star. We show, as an example, how the positions of the frequencies of the p-modes changes from the familiar “picket fence” or regular spacing to a more random irregular spacing as the sun evolves from the ZAMS to the base of the giant branch. For α Cen, e Eri, Procyon, Arcturus, and μ Cas we describe, in specific terms, how the frequency spacings can be used to improve our knowledge about each of these stars. We discuss the important advantages of observing the p-modes of stars in star clusters. We also discuss how rotational splittings could be used along with other stellar diagnostics to infer the rotational history of the star's interior.

We have detected radial velocity variations in Arcturus (K1 IIIb) spanning a total range of at least 160 m/s, more than 8 times the nightly standard deviation of measurements made during the same season (often on the same nights) on the star Pollux. The velocities of Arcturus tend to alternate between two values separated by 60–100 m/s from night to night. A periodogram of 32 nightly velocity averages spanning 100 days shows significant power (false alarm probability less than 1%) for a period of 2.18 days, and its alias of 1.84 days. Although these periods are close to the Nyquist period of 2.00 days, there is no preference for periods of exactly 2 solar or 2 sidereal days. Another consequence of the aliasing is that periods of 1/3 these values cannot be ruled out. Exhaustive checks indicate no evidence that these variations are terrestrial or instrumental in origin.

Recent observations concerning the depth dependence of motions in stellar atmospheres are reviewed. With regard to turbulence in stellar photospheres, attention is given to evidence from the sun and Arcturus for an increase in the total micro- plus macro-velocities with height, starting at mid-photospheric levels. Concerning stellar chromospheric velocity fields, it is noted that Mg II data point to changes in the hydrodynamic structure of the upper atmosphere. Ca II and Mg II asymmetry observations and other studies are used to describe the upper atmospheric structure of cool evolved stars, particularly coronae and circumstellar envelopes, revealing a depth dependent effect of velocity fields among a wide range of such stars.

Simultaneous spectrometric and photometric observations have been performed, on the red giant star Arcturus (α Boo), in a search for radial velocity or luminosity variations related to global oscillations of the stellar structure. From a preliminary analysis of the spectrometric data, several frequencies have been discovered in the range from 1 to 50 μHz, the highest amplitude being of ∼60 ms−1 at 4.3 μHz. From the analysis of the photometric data, slight evidence of this variation has been found, yielding a value of ΔV/Δm=48 km s−1 mag−1.

We present abundances for Ru and Hf, compare them to abundances of other heavy elements, and discuss the problems found in determining Ru and Hf abundances with laboratory gf-values in the spectra of barium stars. We determined Ru and Hf abundances in a sample of giant and dwarf barium stars, by the spectral synthesis of two RuI (4080.574A and 4757.856A) and two HfII (4080.437A and 4093.155A) transitions. The stellar spectra were observed with FEROS/ESO, and the stellar atmospheric parameters lie in the range 4300 < Teff/K < 6500, -1.2 < [Fe/H], 11 pages, 7 figures and 7 tables. accepted to A&A

We present new results on oscillations of the K1.5 III giant Arcturus (alpha Boo), from analysis of just over 2.5 yr of precise photometric observations made by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. A strong mode of oscillation is uncovered by the analysis, having frequency 3.51+/-0.03 micro-Hertz. By fitting its mode peak, we are able offer a highly constrained direct estimate of the damping time (tau = 24+/-1 days). The data also hint at the possible presence of several radial-mode overtones, and maybe some non-radial modes. We are also able to measure the properties of the granulation on the star, with the characteristic timescale for the granulation estimated to be 0.50+/-0.05 days., 6 pages, 5 figures; accepted for publication in MNRAS Letters

The three Mn I lines at 17325, 17339 and 17349 \AA~are among the 25 strongest lines ($\log(gf)>0.5$) in the H-band. They are all heavily broadened due to hyperfine structure and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infra-red (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines can not be described in the conventional way by the diagonal $A$ and $B$ hyperfine interaction constants. The off-diagonal hyperfine interaction not only has large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and $gf$-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, agreement between our synthetic and experimental spectra was achieved. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modelled in the relevant region, $1.73-1.74$ $\mu$m using our theoretically predicted $gf$-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and $gf$-values for all the $3d^54s({^7S})4d$ e$^{6}$D $-$ $3d^54s({^7S})4f$ w$^{6}$F hyperfine lines are available as supplementary material online, whereas only the stronger lines are presented and discussed in detail in this paper., Comment: 24 pages, 6 figures, 3 tables (more data tables will be available online when published in Astrophysical Journal Supplement Series)

We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (~ -0.1 dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements - Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H] = 0.03 +/- 0.07 dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11 +/- 0.05 dex). We also find the neutron-capture element barium to be highly enhanced - [Ba/Fe] = +0.48 +/- 0.08 - and disparate from cluster measurements of neutron-capture elements La and Zr (-0.08 +/- 0.05 and 0.08 +/- 0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments., 15 pages, 9 figures, Table 1 typo fixed

We present near-IR interferometric measurements of the K1.5 giant Arcturus (alpha Bootis), obtained at the IOTA interferometer with the FLUOR instrument, in four narrow filters with central wavelengths ranging from 2.03 to 2.39 micron. These observations were expected to allow us to quantify the wavelength dependence of the diameter of a typical K giant. They are compared to predictions from both plane-parallel and spherical model atmospheres. Unexpectedly, neither can explain the observed visibilities. We show how these data suggest the presence of a companion, in accordance with the Hipparcos data on this star, and discuss this solution with respect to Arcturus' single star status., Comment: 15 pages, 14 figures, accepted for publication by Astronomy & Astrophysics

The Great Sagittarius Star Cloud, north of Gamma (γ) and Delta (δ) Sagittarii, is the brightest of all the Milky Way star clouds. It is so bright because it is a section of our Galaxy’s central bulge which we see over the thick dust of the Sagittarius Rift. Bays of Sagittarius Rift dust can be traced with giant binoculars along the NW side of the star cloud; and a fairly conspicuous triangular extension of the star cloud juts into the Sgr Rift SE of the 4th magnitude Cepheid variable X Sgr. However, the opposite side of the star cloud, to the SE, fades away gradually (as indeed does the periphery of the whole Galactic bulge, if we could see it). A semi-detached lobe of the Great Sgr Star Cloud is centered midway between Epsilon (e) Sagittarii and the open cluster M6 in Scorpius; and, further SW, the Milky Way glow behind the 80′-diameter open cluster M7 is actually another part of the Galaxy’s bulge. We know that these two small star clouds are sections of the bulge because on color photos they have the same yellowish color as the Great Sgr Star Cloud itself. Studies of the bulge have shown that most of its light comes from K-type giants like Arcturus, stars with a yellow-orange or golden-yellow color.

Here, we report on our detection of water vapor in the mid-infrared (11-12 microns) spectrum of the Kl.5 giant Arcturus (α Boo) obtained with the high-resolution, infrared spectrograph TEXES. The detection is presented in detail in Ryde et al. 2002 ApJ, submitted. We are successful in modeling several resolved, rotational lines of water vapor and vibration-rotational (1.5 microns) and rotational lines of OH with a modified MARCS photosphere

The best hope of finding Earth-like planets around Sun-like stars lies not in Doppler spectroscopy, stellar occultation, water maser detection, or even direct imaging via telescopic ground arrays: it’s in the ancient art of astrometry. Astrometry has long been a tedious and painstaking method of measuring a star’s position, distance, and its proper motion (essentially its movement across our line of sight). In the second century B.C., without the benefit of binoculars or a telescope, the Greek astronomer Hipparchus spent years producing a catalog of over 1,000 star positions. Almost two millennia later, in 1718, Edmund Halley (whose name would later become inextricably linked with the comet) found that three stars—including Arcturus, a northern star that Hipparchus had recorded—had changed their positions on the sky by several fractions of a degree. Halley compared his findings against measurements compiled by Ptolemy, the Egyptian astronomer, who had assembled the work of Hipparchus and others in the Almagest, an astronomical compendium published two centuries after the birth of Christ. Halley’s assumption that the stars must be moving across our line of sight marked the birth of modem astrometry.

New red and violet system line lists for the CN isotopologues {sup 13}C{sup 14}N and {sup 12}C{sup 15}N have been generated. These new transition data are combined with those previously derived for {sup 12}C{sup 14}N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values.

In this study we cross-correlate many IUE echellograms of a variety of stars to evaluate systematic error sources in the wavelength zeropoint of all three cameras. We first evaluated differences between the final archived ("NEWSIPS") and the originally processed ("IUESIPS") spectra. These show a clear time dependence in zeropoint for the SWP camera due to revisions in the IUESIPS wavelength scale. Small IUESIPS - NEWSIPS differences are also found for the LWR camera. We also examined wavelength zeropoint disparities between data obtained both through the small and large entrance apertures and for observations made by different target acquisition modes for faint and bright stars. We found that velocities resulting from these alternative observing modes are nil. For large-aperture observations the dominant error source is the target position placement in the aperture. We searched for spurious trends with time, and found only a suggestion of time trends for faint stars observed with the SWP camera. We also discovered 1-day, +/-3 km/s sinusoidsal patterns in intensive monitoring data which are ascribable to changes in telescope focus resulting from thermal drifts. In the second part of the paper, we measured mean zeropoint errors of NEWSIPS echellogram data against laboratory results by using the GHRS spectral atlas of the 10 Lac. We find that the derived apparent velocity difference for this star is -1 +/-3.5 km/s. Several less precise comparisons lead to similar results. The zeropoints of the NEWSIPS-processed LWP/LWR cameras are evaluated and are also found to be nearly zero (+/-5 km/s) relative to HST atlases of Arcturus and Procyon atlas. These results do not support result by Gonzalez-Riestra et al. that corrections should be introduced to the wavelength scales of various NEWSIPS high-dispersion data products., Comment: 16 pages, Latex with 12 figures, Accepted by Pub. Astron. Soc. Pacific for July 1, 2001. Files available from ftp://nobel.stsci.edu/pub/iuerv/

The’ solar-stellar connection’ bridges the daytime and nighttime communities; an essential link between the singular, but detailed, views of our Sun, and the broad, but coarse, glimpses of the distant stars. One area in particular — magnetic activity — has profited greatly from the two way traffic in ideas. In that spirit, I present an evolutionary context for coronal activity, focusing on the very different circumstances of low-mass main-sequence stars like the Sun, compared with more massive stars. The former are active mainly very early in their lives, whereas the latter become coronal only near the end of theirs, during the brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow, then red, giants. I describe tools at the disposal of the stellar astronomer; especially spectroscopy in the ultraviolet and X-ray bands where coronae leave their most obvious imprints. I compare HST STIS spectra of solar-type dwarfs — ζ Dor (F7 V), an active coronal source, and α Cen A (G2 V), near twin of the Sun — to the SOHO SUMER UV solar atlas. I also compare the STIS line profiles of the active coronal dwarf to the corresponding features in the mixed activity ‘hybrid chromosphere’ bright giant α TrA (K2II) and the archetype ‘non-coronal’ red giant Arcturus (α Boo; K2 III). The latter shows dramatic evidence for a ‘cool absorber’ in its outer atmosphere that is extinguishing the ‘hot lines’ (like SiIV λ1393 and Nv λ1238) below about 1500 A; the corona of the red giant seems to lie beneath its extended chromosphere, rather than outside as in the Sun. I present an early taste of the moderate resolution spectra we can expect from the recently launched Chandra X-ray Observatory (CXO), and contemporaneous STIS high resolution UV measurements of the CXO calibration star Capella (α Aur; G8 III + Gl III). Last, I describe preliminary results from a May 1999 observing campaign involving SOHO SUMER, TRACE, and the Kitt Peak Infrared Imaging Spectrometer (IRIS). The purpose was to explore the dynamics of the quiet solar atmosphere through the key ‘magnetic transition zone’ that separates the kinetically dominated deep photosphere from the magnetically dominated coronal regime. Linking spatially and temporally resolved solar phenomena to properties of the average line shapes (widths, asymmetries, intensity ratios, and Doppler shifts) is a crucial step in carrying physical insights from the solar setting to the realm of the distant stars.

We implement a least-squares deconvolution (LSD) code to study magnetic fields on cool stars. We first apply our code to high-resolution optical echelle spectra of 53 Cam (a magnetic Ap star) and three well-studied cool stars (Arcturus, 61 Cyg A, and ? Boo A) as well as the Sun (by observing the asteroid Vesta) as tests of the code and the instrumentation. Our analysis is based on several hundred photospheric lines spanning the wavelength range 5000?? to 9000??. We then apply our LSD code to six nights of data on the Classical T Tauri Star BP Tau. A maximum longitudinal field of 370 ? 80 G is detected from the photospheric lines on BP Tau. A 1.8?kG dipole tilted at 129? with respect to the rotation axis and a 1.4?kG octupole tilted at 104? with respect to the rotation axis, both with a filling factor of 0.25, best fit our LSD Stokes V profiles. Measurements of several emission lines (He I?5876??, Ca II 8498??, and 8542??) show the presence of strong magnetic fields in the line formation regions of these lines, which are believed to be the base of the accretion footpoints. The field strength measured from these lines shows night-to-night variability consistent with rotation of the star.

Multi-wavelength centimeter continuum observations of non-dusty, non-pulsating K spectral-type red giants directly sample their chromospheres and wind acceleration zones. Such stars are feeble emitters at these wavelengths however, and previous observations have provided only a small number of modest S/N measurements slowly accumulated over three decades. We present multi-wavelength Karl G. Jansky Very Large Array thermal continuum observations of the wind acceleration zones of two dust-free red giants, Arcturus (Alpha Boo: K2 III) and Aldebaran (Alpha Tau: K5 III). Importantly, most of our observations of each star were carried out over just a few days, so that we obtained a snapshot of the different stellar atmospheric layers sampled at different wavelengths, independent of any long-term variability. We report the first detections at several wavelengths for each star including a detection at 10 cm (3.0 GHz: S band) for both stars and a 20 cm (1.5 GHz: L band) detection for Alpha Boo. This is the first time single luminosity class III red giants have been detected at these continuum wavelengths. Our long-wavelength data sample the outer layers of Alpha Boo's atmosphere where its wind velocity is approaching its terminal value and the ionization balance is becoming frozen-in. For Alpha Tau, however, our long-wavelength data are still sampling its inner atmosphere, where the wind is still accelerating probably due to its lower mass-loss rate. We compare our data with published semi-empirical models based on ultraviolet data, and the marked deviations highlight the need for new atmospheric models to be developed. Spectral indices are used to discuss the possible properties of the stellar atmospheres, and we find evidence for a rapidly cooling wind in the case of Alpha Boo. Finally, we develop a simple analytical wind model for Alpha Boo based on our new long-wavelength flux measurements.

We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent Non-Local Thermodynamic Equilibrium (NLTE), and compare them to the LTE grid of Short & Hauschildt (2010) (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T(tau) relation) and the SED as a finely sampled function of Teff, log g, and [A/H] among solar metallicity and mildly metal poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best fit Teff values that are ~30 to 90 K lower than those provided by LTE models, while providing greater consistency between \log g values, and, for Arcturus, Teff values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best fit Teff values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant.

Context. Arcturus is the second closest K giant and among the brightest stars in the sky. It has not been found to have a magnetic field, even though Ca ii H&K lines as activity indicators imply that Arcturus is magnetically active.Aims. We measure the mean longitudinal magnetic field strengths and interpret them in terms of an intraseasonal activity modulation.Methods. We apply our new Zeeman component decomposition (ZCD) technique to three single sets of Stokes I and V spectra to measure the longitudinal component of the magnetic field responsible for tiny Zeeman signatures detected in spectral line profiles.Results. For two of the spectra, we report the detection of the Zeeman signature of a weak longitudinal magnetic field of 0.65 ± 0.26 G and 0.43 ± 0.16 G. The third measurement is less significant, but all the measurements closely reproduce a rotationally modulated activity cycle with four active longitudes. Conclusions. For the first time, a magnetic field on Arcturus is directly detected. This field can be attributed to a diminishing solar-type α Ω-dynamo acting in the deepening convection zone of Arcturus. We demonstrate that our new method ZCD lowers the detection limit of very weak magnetic fields from spectropolarimetric measurements.

Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths. Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13 997 angstrom, 15 of which are in the infrared. The transitions at 12 899 angstrom and 12 975 angstrom are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I lines in spectra of late-type stars. Using the new experimentally measured Mn I log(gf) values together with existing data for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = -6.65 +/- 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 +/- 0.20 in the atmosphere of Arcturus, and log N(Mn) = -6.70 +/- 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150. (Less)

This dissertation presents an analysis of data obtained from long-term spectroscopic monitoring of the bright, nearby K giant star Arcturus (a Bootis, K1.5 III, HR 5340, HD 124897), conducted using the University of Western Ontario’s Elginfield Observatory. Over 1300 high-resolution spectra ( ) 5 l/Dl ≈ 10 were recorded in the 6250 A spectral region during the 1984– 2006 observing seasons, with 311 simultaneous, precise radial velocity measurements (j ∼ 25 m s ) obtained during the 2002–2006 observing seasons. Temperature variations were measured using the well-established line-depth ratio V i l6251.83 to Fe i l6252.56. Velocity spans were obtained from the line bisector of the Fe i l6252.56 line. Precise radial velocities were measured using the telluric absorption technique outlined by Gray & Brown (2006, PASP, 118, 399). Spectroscopic observations and precise radial velocity measurements reveal variability in Arcturus from hours to years. From velocity span observations, three distinct periods of variability are observed: (1) a semiregular 5 1 yr period interpreted as evidence for a long-term stellar magnetic cycle, (2) a 2.0 0.2 yr modulation identified as the rotation period (see also Gray & Brown 2006, PASP, 118, 1112), and (3) a semicoherent 200 5 day period interpreted as one-fourth of the rotation period, indicating the presence of four magnetically active longitudes on the surface of Arcturus. One of these four active longitudes is postulated to dominate the other three, inducing the observed 2 yr rotational modulation in the velocity span measurements. Line-depth ratio measurements indicate no evidence for variations in temperature in excess of 10 K over the observed magnetic cycle, rotation period, and short-term variability of Arcturus. Precise radial velocity measurements exhibit a long-term period of 222 3 days, with an amplitude of 150 20 m s . This long-term period and the corresponding amplitude are consistent with the radial velocity observations of Hatzes & Cochrane (1993, ApJ, 413, 339). The 222 day period is coherent over the 14 yr time span between the Hatzes & Cochrane (1993, ApJ, 413, 339) data and the observations of this work, and does not correlate with observed line bisector or line-depth ratio variations, suggesting that this observed period is not associated with stellar variability. Hatzes & Cochrane (1993, ApJ, 413, 339) suggested that the observed long-term radial velocity period was due either to rotational modulation or a low-mass companion, but were unable to differentiate between the two explanations, due to a lack of ancillary spectroscopic data. A detection of a low-mass companion is postulated by this work. Assuming a mass of 1 M, for Arcturus, a best-fit Keplerian orbit to the 222 day period is found to have approximately zero eccentricity, a projected semimajor axis ( ) of 0.72 AU, and a companion a sin i mass ( ) of ≥4.4 MJ. M sin i 2 Precise radial velocity observations also demonstrate a scatter (j) of ∼145 m s 1 superimposed on the observed 222 day period, resulting from short-term variability on the timescale of individual nights to days. This short-term variability has been interpreted as being the result of solar-type p-mode oscillations by previous studies, such as Hatzes & Cochrane (1994, ApJ, 422, 366), Merline (1995, Ph.D. thesis, Univ. Arizona), and Retter et al. (2003, ApJ, 591, L151). Observed scatter during individual nights ranges from ∼50 to 180 m s , while the scatter over consecutive nights ranges from ∼70 to 160 m s . These observations are consistent with previous studies of the short-term radial velocity variability of Arcturus. Ultimately, this scatter of ∼145 m s 1 limits the accuracy of studies of the long-term radial velocity variability of Arcturus. Evidence for eruptive events is also suggested from the observed radial velocities.