Saint Mary's Faculty Articles and Other Workshttp://library2.smu.ca:80/handle/01/218802018-02-24T00:34:12Z2018-02-24T00:34:12ZThe pulsation mode of the Cepheid PolarisTurner, David Gerald, 1945-Kovtyukh, V. V.Usenko, I. A.Gorlova, N. I.http://library2.smu.ca:80/handle/01/272872018-02-23T18:00:41Z2013-01-01T00:00:00ZThe pulsation mode of the Cepheid Polaris
A previously derived photometric parallax of 10.10[plus or minus]0.20 mas, d = 99[plus or minus]2 pc, is confirmed for Polaris by a spectroscopic parallax derived using line ratios in high dispersion spectra for the Cepheid. The resulting estimates for the mean luminosity of M[subscript V] = −3.07[plus or minus]0.01 s.e., average effective temperature of T[subscript eff] = 6025[plus or minus]1Ks.e., and intrinsic color of (B−V)0 = [subscript plus]0.56[plus or minus]0.01 s.e., which match values obtained previously from the photometric parallax for a space reddening of E[subscript B−V] = 0.02[plus or minus]0.01, are consistent with fundamental mode pulsation for Polaris and a first crossing of the instability strip, as also argued by its rapid rate of period increase. The systematically smaller Hipparcos parallax for Polaris appears discrepant by comparison.
2013-01-01T00:00:00ZThe pulsation mode and distance of the Cepheid FF AquilaeTurner, David Gerald, 1945-Kovtyukh, V. V.Luck, R. E.Berdnikov, L. N.http://library2.smu.ca:80/handle/01/272862018-02-23T16:00:43Z2013-01-01T00:00:00ZThe pulsation mode and distance of the Cepheid FF Aquilae
The determination of pulsation mode and distance for field Cepheids is a complicated problem best resolved by a luminosity estimate. For illustration a technique based on spectroscopic luminosity discrimination is applied to the 4.47 day s-Cepheid FF Aql. Line ratios in high dispersion spectra of the variable yield values of MV = −3.40 [plus or minus] 0.02 s.e. ([plus or minus]0.04 s.d.), average effective temperature T[subscript eff] = 6195 [plus or minus] 24 K, and intrinsic color ( B − V )0 = +0.506[plus or minus]0.007, corresponding to a reddening of E[subscript B−V] = 0.25[plus or minus]0.01, or E[subscript B−V] (B0) = 0.26[plus or minus]0.01. The skewed light curve, intrinsic color, and luminosity of FF Aql are consistent with fundamental mode pulsation for a small-amplitude classical Cepheid on the blue side of the instability strip, not a sinusoidal pulsator. A distance of 413 [plus or minus] 14 pc is estimated from the Cepheid’s angular diameter in conjunction with a mean radius of R = 39.0 ± 0.7R inferred from its luminosity and effective temperature. The dust extinction toward FF Aql is described by a ratio of total-to-selective extinction of R[subscript V] = A[subscript V] /E(B − V ) = 3.16 [plus or minus] 0.34 according to the star’s apparent distance modulus.
2013-01-01T00:00:00ZMOST detects transits of HD 97658b, a warm, likely volatile-rich super-EarthDragomir, DianaMatthews, Jaymie M.Eastman, Jason D.Cameron, ChrisHoward, Andrew W.Guenther, David B.Kuschnig, RainerMoffat, Anthony F. J.Rowe, Jason F.Rucinski, Slavek M.http://library2.smu.ca:80/handle/01/272852018-02-23T14:19:22Z2013-01-01T00:00:00ZMOST detects transits of HD 97658b, a warm, likely volatile-rich super-Earth
Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope, we have found that this exoplanet transits with an ephemeris consistent with that predicted from radial velocity measurements. The mid-transit times are 5.6[sigma] earlier than those of the unverified transit-like signals reported in 2011, and we find no connection between the two sets of events. The transit depth together with our determined stellar radius (R[subscript star] = 0.703[superscript +0.039 subscript−0.034] R[circled dot]) indicates a 2.34[superscript+0.18 subscript−0.15] R[subscript circled plus] super-Earth.When combined with the radial velocity determined mass of 7.86 [plus or minus] 0.73 M[subscript circled plus], our radius measure allows us to derive a planet density of 3.44[superscript+0.91 subscript−0.82] g cm[superscript−3]. Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements. The star of the HD 97658 system is the second brightest known to host a transiting super-Earth, facilitating follow-up studies of this not easily daunted, warm and likely volatile-rich exoplanet.
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2013-01-01T00:00:00ZModeling the near-ultraviolet band of gk stars. III. dependence on abundance patternShort, C. Ian (Christopher Ian), 1965-Campbell, Eamonn A.http://library2.smu.ca:80/handle/01/272842018-02-22T20:37:43Z2013-01-01T00:00:00ZModeling the near-ultraviolet band of gk stars. III. dependence on abundance pattern
We extend the grid of non-LTE (NLTE) models presented in Paper II to explore variations in abundance pattern
in two ways: (1) the adoption of the Asplund et al. (GASS10) abundances, (2) for stars of metallicity, [M/H], of
−0.5, the adoption of a non-solar enhancement of [alpha]-elements by +0.3 dex. Moreover, our grid of synthetic spectral
energy distributions (SEDs) is interpolated to a finer numerical resolution in both T[subscript eff] ([delta]T[subscript eff] = 25 K) and log g ([delta] log g = 0.25). We compare the values of T[subscript eff] and log g inferred from fitting LTE and NLTE SEDs to observed SEDs throughout the entire visible band, and in an ad hoc “blue” band. We compare our spectrophotometrically derived T[subscript eff] values to a variety of T[subscript eff] calibrations, including more empirical ones, drawn from the literature. For stars of solar metallicity, we find that the adoption of the GASS10 abundances lowers the inferred T[subscript eff] value by 25–50 K for late-type giants, and NLTE models computed with the GASS10 abundances give T[subscript eff] results that are marginally in better agreement with other T[subscript eff] calibrations. For stars of [M/H] = −0.5 there is marginal evidence that adoption of [alpha]-enhancement further lowers the derived T[subscript eff] value by 50 K. Stellar parameters inferred from fitting NLTE models to SEDs are more dependent than LTE models on the wavelength region being fitted, and we find that the effect depends on how heavily line blanketed the fitting region is, whether the fitting region is to the blue of the Wien peak of the star’s SED, or both.
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2013-01-01T00:00:00ZHybrid cosmological simulations with stream velocitiesRichardson, Mark L. A.Scannapieco, EvanThacker, Robert John, 1970-http://library2.smu.ca:80/handle/01/272832018-02-21T18:00:25Z2013-01-01T00:00:00ZHybrid cosmological simulations with stream velocities
In the early universe, substantial relative “stream” velocities between the gas and dark matter arise due to radiation pressure and persist after recombination. To assess the impact of these velocities on high-redshift structure formation, we carry out a suite of high-resolution adaptive mesh refinement (AMR) cosmological simulations, which use smoothed particle hydrodynamic data sets as initial conditions, converted using a new tool developed for this work. These simulations resolve structures with masses as small as a few 100 M[circled dot], and we focus on the 10[superscript 6] M[circled dot] “mini-halos” in which the first stars formed. At z ≈ 17, the presence of stream velocities has only a minor effect on the number density of halos below 10[superscript 6] M[circled dot], but it greatly suppresses gas accretion onto all halos and the dark matter structures around them. Stream velocities lead to significantly lower halo gas fractions, especially for ≈10[superscript 5] M[circled dot] objects, an effect that is likely to depend on the orientation of a halo’s accretion lanes. This reduction in gas density leads to colder, more compact radial profiles, and it substantially delays the redshift of collapse of the largest halos, leading to delayed star formation and possibly delayed reionization. These many differences suggest that future simulations of early cosmological structure formation should include stream velocities to properly predict gas evolution, star formation, and the epoch of reionization.
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2013-01-01T00:00:00Zgamma Doradus pulsation in two pre-main sequence stars discovered by CoRoTZwintz, K.Fossati, L.Ryabchikova, T.Kaiser, A.Gruberbauer, MichaelBarnes, T. G.Baglin, A.Chaintreuil, S.http://library2.smu.ca:80/handle/01/272822018-02-22T13:50:29Z2013-01-01T00:00:00Zgamma Doradus pulsation in two pre-main sequence stars discovered by CoRoT
Context. Pulsations in pre-main sequence stars have been discovered several times within the last years. But nearly all of these pulsators are of [delta] Scuti-type. [gamma] Doradus-type pulsation in young stars has been predicted by theory, but lack observational evidence. Aims. We present the investigation of variability caused by rotation and ([gamma] Doradus-type) pulsation in two pre-main sequence members of the young open cluster NGC 2264 using high-precision time series photometry from the CoRoT satellite and dedicated high-resolution spectroscopy. Methods. The variability found using the CoRoT data was combined with the fundamental parameters and chemical abundances derived from high-resolution spectroscopy, obtained at the Mc Donald Observatory, to discuss the presence of pulsation and rotation in the two NGC2264 cluster members. Time series photometry of NGC2264 VAS 20 and NGC2264 VAS 87 was obtained by the
CoRoT satellite during the dedicated short run SRa01 in March 2008. NGC2264 VAS 87 was re-observed by CoRoT during the short run SRa05 in December 2011 and January 2012. Frequency analysis was conducted using Period04 and SigSpec. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. The frequency analysis yielded ten (NGC2264 VAS 20) and fourteen (NGC2264 VAS 87) intrinsic frequencies in the range from 0 to 1.5 d[superscript −1], which are attributed to be caused by a combination of rotation and pulsation. The effective temperatures were derived to be 6380 [plus or minus] 150 K for NGC2264 VAS 20 and 6220 [plus or minus] 150 K for NGC2264 VAS 87. Membership of the two stars to the cluster is confirmed independently using X-ray fluxes, radial velocity measurements, and proper motions available in the literature. The derived lithium abundances of log n(Li) = 3.34 and 3.54 for NGC 2264 VAS 20 and NGC2264 VAS 87 agree with the lithium abundance for other stars in NGC2264 of similar T[subscript eff] reported in the literature. Conclusions. We conclude that the two objects are members of NGC 2264 and therefore are in their pre-main sequence evolutionary stage. Their variability is attributed to be caused by rotation and g-mode pulsation rather than rotation only. Assuming that part of their variability is caused by pulsation, these two stars might be the first pre-main sequence [gamma] Doradus candidates.
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2013-01-01T00:00:00ZOn the form of the Spitzer Leavitt Law and its dependence on metallicityMajaess, Daniel J.Turner, David Gerald, 1945-Gieren, W.http://library2.smu.ca:80/handle/01/272812018-02-22T15:22:33Z2013-08-01T00:00:00ZOn the form of the Spitzer Leavitt Law and its dependence on metallicity
The form and metallicity dependence of Spitzer mid-infrared Cepheid relations are a source of debate. Consequently, Spitzer 3.6 and 4.5 [mu]m period–magnitude and period–color diagrams were re-examined via robust routines, thus providing an alternative interpretation to consider. The relations (nearly mean-magnitude) appear nonlinear over an extensive baseline (0.45 < log P[subscript 0] < 2.0), particularly the period–color trend, which to first order follows constant (3.6–4.5) color for shorter-period Cepheids and may transition into a bluer convex trough at longer periods. The period–magnitude functions can be described by polynomials (e.g., [3.6 [mu]m] = K[subscript 0] − (3.071 [plus or minus] 0.059) log P[subscript 0] − (0.120 [plus or minus] 0.032) log P[subscript 0] [superscript 2]), and Cepheid distances computed using 3.6 and 4.5 [mu]m relations agree with each other and the latter provides a first-order consistency check (CO sampled at 4.5 [mu]m does not seriously compromise those distances). The period–magnitude relations appear relatively insensitive to metallicity variations ([Fe/H] ∼ 0 to −0.75 |[gamma] | < 0.1 mag dex[superscript −1]), a conclusion inferred partly from comparing galaxy distances established from those relations and NED-D (n > 700), yet a solid conclusion awaits comprehensive mid-infrared observations for metal-poor Cepheids in IC 1613 ([Fe/H] ∼ −1). The Cepheid-based distances were corrected for dust obscuration using a new ratio (i.e., A[subscript 3.6]/E[subscript B−V] = 0.18 [plus or minus] 0.06) deduced from GLIMPSE (Spitzer) data.
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2013-08-01T00:00:00ZRegular frequency patterns in the young [delta] Scuti star HD 261711 observed by the CoRoT and MOST satellitesZwintz, K.Fossati, L.Guenther, David B.Ryabchikova, T.Baglin, A.Themessl, N.Barnes, T. G.Matthews, J. M.Auvergne, M.Bohlender, D.http://library2.smu.ca:80/handle/01/272802018-02-22T13:58:01Z2013-04-01T00:00:00ZRegular frequency patterns in the young [delta] Scuti star HD 261711 observed by the CoRoT and MOST satellites
Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars. Aims. We concentrate on an asteroseismological study of HD261711, a rather hot [delta] Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD261711 was discovered to be a PMS [delta] Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods. High-precision, time-series photometry of HD261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star’s fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the [delta] Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new [delta] Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (T[subscript eff]) was derived to be 8600 [plus or minus] 200 K, log g is 4.1 [plus or minus] 0.2, and the projected rotational velocity ([upsilon] sin i) is 53 [plus or minus] 1 km s[superscript −1]. Using our T[subscript eff] value and the radius of 1.8 [plus or minus] 0.5 R[subscript circled dot] derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L[subscript circled dot] of 1.20 [plus or minus] 0.14 which agrees well to the seismologically determined values of 1.65 R[subscript circled dot] and, hence, a log L/L[subscript circled dot] of 1.13. The radial velocity of 14 [plus or minus] 2 km s[superscript −1] we derived for HD261711, confirms the star’s membership to NGC2264. Conclusions. Our asteroseismic models suggest that HD261711 is a [delta] Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9 M[subscript circled dot]. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes.
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2013-04-01T00:00:00ZThe asymmetric drift, the local standard of rest, and implications from RAVE dataGolubov, O.Just, A.Bienayme, O.Bland-Hawthorn, J.Gibson, Brad K.Grebel, E. K.Munari, U.Navarro, J. F.Parker, Q.Seabroke, G.http://library2.smu.ca:80/handle/01/272792018-02-20T20:58:00Z2013-09-01T00:00:00ZThe asymmetric drift, the local standard of rest, and implications from RAVE data
Context. The determination of the local standard of rest (LSR), which corresponds to the measurement of the peculiar motion of the Sun based on the derivation of the asymmetric drift of stellar populations, is still a matter of debate. The classical value of the tangential peculiar motion of the Sun with respect to the LSR was challenged in recent years, claiming a significantly larger value.
Aims. We present an improved Jeans analysis, which allows a better interpretation of the measured kinematics of stellar populations in the Milky Way disc. We show that the Radial Velocity Experiment (RAVE) sample of dwarf stars is an excellent data set to derive tighter boundary conditions to chemodynamical evolution models of the extended solar neighbourhood. Methods. We propose an improved version of the Strömberg relation with the radial scalelengths as the only unknown.We redetermine the asymmetric drift and the LSR for dwarf stars based on RAVE data. Additionally, we discuss the impact of adopting a different LSR value on the individual scalelengths of the subpopulations.
Results. Binning RAVE stars in metallicity reveals a bigger asymmetric drift (corresponding to a smaller radial scalelength) for more metal-rich populations. With the standard assumption of velocity-dispersion independent radial scalelengths in each metallicity bin, we redetermine the LSR. The new Strömberg equation yields a joint LSR value of V[subscript circled dot] = 3.06 [plus or minus] 0.68 km s[superscript −1], which is even smaller than the classical value based on Hipparcos data. The corresponding radial scalelength increases from 1.6 kpc for the metal-rich bin to 2.9 kpc for the metal-poor bin, with a trend of an even larger scalelength for young metal-poor stars. When adopting the recent Schönrich value of V[subscript circled dot] = 12.24 km s[superscript −1] for the LSR, the new Strömberg equation yields much larger individual radial scalelengths of the RAVE subpopulations, which seem unphysical in part. Conclusions. The new Strömberg equation allows a cleaner interpretation of the kinematic data of disc stars in terms of radial scalelengths. Lifting the LSR value by a few km s[superscript−1] compared to the classical value results in strongly increased radial scalelengths with a trend of smaller values for larger velocity dispersions.
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2013-09-01T00:00:00ZThe distance to the young open cluster Westerlund 2Carraro, G.Turner, David Gerald, 1945-Majaess, Daniel J.Baume, G.http://library2.smu.ca:80/handle/01/272782018-02-20T20:27:50Z2013-07-01T00:00:00ZThe distance to the young open cluster Westerlund 2
A new X-ray, UBVRI[subscript c], and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepancies tied to the cluster’s distance. Existing spectroscopic observations for bright cluster members and new multi-band photometry imply a reddening relation toward Westerlund 2 described by E[subscript U−B]/E[subscript B−V] = 0.63 + 0.02 E[subscript B−V]. Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fitting yield values of R[subscript V] = A[subscript V]/E[subscript B−V] = 3.88 [plus or minus] 0.18 and 3.77 [plus or minus] 0.19, respectively, and confirm prior assertions that anomalous interstellar extinction is widespread throughout Carina. The results were confirmed by applying the color-difference method to UBVRI[subscript c]JHK[subscript s] data for 19 spectroscopically observed cluster members, yielding RV = 3.85 [plus or minus] 0.07. The derived distance to Westerlund 2 of d = 2.85 [plus or minus] 0.43 kpc places the cluster on the far side of the Carina spiral arm. The cluster’s age is no more than [tau] [approximately equal to] 2 × 10[superscript 6] yr as inferred from the cluster’s brightest stars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are very likely cluster members, and their inferred luminosities are consistent with those of other late-WN stars in open clusters. The color–magnitude diagram for Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolute magnitudes that might be linked to close binary mergers. These features, in conjunction with the evidence for mass loss from the WR stars, may help to explain the high flux of [gamma]-rays, cosmic rays, and X-rays from the direction toward Westerlund 2.
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2013-07-01T00:00:00Z