Saint Mary's Faculty Articles and Other Workshttp://library2.smu.ca:80/handle/01/218802017-04-24T22:17:16Z2017-04-24T22:17:16ZNLTE AND LTE Lick indices for red giants from [Fe/H] 0.0 TO −6.0 AT SDSS AND IDS spectral resolutionShort, C. Ian (Christopher Ian), 1965-Young, Mitchell E.Layden, Nicholashttp://library2.smu.ca:80/handle/01/268832017-04-24T19:55:23Z2015-09-01T00:00:00ZNLTE AND LTE Lick indices for red giants from [Fe/H] 0.0 TO −6.0 AT SDSS AND IDS spectral resolution
We investigate the dependence of the complete system of 22 Lick indices on overall metallicity scaled from solar abundances, [M/H], from the solar value, 0.0, down to the extremely metal-poor (XMP) value of −6.0, for late-type giant stars (MK luminosity class III, log g = 2.0) of MK spectral class late-K to late-F (3750 < T[subscript eff] < 6500 K) of the type that are detected as “fossils” of early galaxy formation in the Galactic halo and in extra-galactic structures. Our investigation is based on synthetic index values, I, derived from atmospheric models and synthetic spectra computed with PHOENIX in Local Thermodynamic Equilibrium (LTE) and Non-LTE (NLTE), where the synthetic spectra have been convolved to the spectral resolution, R, of both IDS and SDSS (and LAMOST) spectroscopy. We identify nine indices, that we designate “Lick-XMP,” that remain both detectable and signiﬁcantly [M/H]-dependent down to [M/H] values of at least ~ -5.0, and down to [M/H] ~ -6.0 in ﬁve cases, while also remaining well-behaved (single-valued as a function of [M/H] and positive in linear units). For these nine indices, we study the dependence of I on NLTE effects, and on spectral resolution. For our LTE I values for spectra of SDSS resolution, we present the ﬁtted polynomial coefﬁcients, C[subscript n], from multi-variate linear regression for I with terms up to third order in the independent variable pairs (T[subscript eff], [M/H]) and (V - K, [M/H]), and compare them to the ﬁtted C[subscript n] values of Worthey et al. at IDS spectral resolution. For this ﬁtted I data-set we present tables of LTE partial derivatives, [partial derivative]I/[partial derivative]T[subscript eff][vertical bar][M/H], [partial derivative]I/[partial derivative][M/H][vertical bar] T[subscript eff], [partial derivative]∣/[partial derivative](V - K) [vertical bar][M/H] and [partial derivative]I/[partial derivative][M/H](V - K), that can be used to infer the relation between a given difference, [delta]I, and a difference [delta]T[subscript eff] or [delta](V - K), or a difference [delta][M/H], while the other parameters are held ﬁxed. For Fe-dominated Lick indices, the effect of NLTE is to generally weaken the value of I at any given T[subscript eff] and [M/H] values. As an example of the impact on stellar parameter estimation, for late-type giants of inferred T[subscript eff] [greater than or similar to] 4200 K, an Fe-dominated I value computed in LTE that is too strong might be compensated for by inferring a T[subscript eff] value that is too large.
Publisher's version/PDF
2015-09-01T00:00:00ZNew constraints on the black hole low/hard state inner accretion flow with NuSTARMiller, J. M.Tomsick, J. A.Bachetti, M.Wilkins, D.Boggs, S. E.Christensen, F. E.Craig, W. W.Fabian, A. C.Grefenstette, B. W.Hailey, C. J.http://library2.smu.ca:80/handle/01/268762017-04-13T16:04:00Z2015-01-20T00:00:00ZNew constraints on the black hole low/hard state inner accretion flow with NuSTAR
We report on an observation of the Galactic black hole candidate GRS 1739−278 during its 2014 outburst, obtained with NuSTAR. The source was captured at the peak of a rising “low/hard” state, at a ﬂux of ~0.3 Crab. A broad, skewed iron line and disk reﬂection spectrum are revealed. Fits to the sensitive NuSTAR spectra with a number of relativistically blurred disk reﬂection models yield strong geometrical constraints on the disk and hard X-ray “corona.” Two models that explicitly assume a “lamp post” corona ﬁnd its base to have a vertical height above the black hole of h = 5[superscript +7][subscript −2] GM/c[superscript 2] and h = 18 [plus or minus] 4 GM/c[superscript 2] (90% conﬁdence errors); models that do not assume a “lamp post” return emissivity proﬁles that are broadly consistent with coronae of this size. Given that X-ray microlensing studies of quasars and reverberation lags in Seyferts ﬁnd similarly compact coronae, observations may now signal that compact coronae are fundamental across the black hole mass scale. All of the models ﬁt to GRS 1739−278 ﬁnd that the accretion disk extends very close to the black hole—the least stringent constraint is r[subscript in] = 5[superscript +3][subscript −4] GM/c[superscript 2]. Only two of the models deliver meaningful spin constraints, but a = 0.8 [plus or minus] 0.2 is consistent with all of the ﬁts. Overall, the data provide especially compelling evidence of an association between compact hard X-ray coronae and the base of relativistic radio jets in black holes.
Publisher's version/PDF
2015-01-20T00:00:00ZThe VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulgeDekany, I.Minniti, D.Majaess, Daniel J.Zoccali, M.Hajdu, G.Alonso-Garcia, J.Catelan, M.Gieren, W.Borissova, J.http://library2.smu.ca:80/handle/01/268752017-04-12T19:39:31Z2015-10-20T00:00:00ZThe VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulge
Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy’s evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years.
Publisher's version/PDF
2015-10-20T00:00:00ZCharacterizing K2 planet discoveries: a super-Earth transiting the bright K dwarf HIP 116454Vanderburg, AndrewMontet, Benjamin T.Johnson, John AsherBuchhave, Lars A.Zeng, LiPepe, FrancescoCameron, Andrew CollierLatham, David W.Molinari, EmilioUdry, StephaneGuenther, David B.http://library2.smu.ca:80/handle/01/268732017-04-12T15:58:23Z2015-02-10T00:00:00ZCharacterizing K2 planet discoveries: a super-Earth transiting the bright K dwarf HIP 116454
We report the ﬁrst planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 [plus or minus] 5.4 pc. Based on high-resolution optical spectroscopy, we ﬁnd that the host star is metal-poor with [Fe/H] = −0.16 [plus or minus] 0.08 and has a radius R[subscript star] = 0.716 [plus or minus] 0.024 R[subscript circled dot] and mass M[subscript star] = 0.775 [plus or minus] 0.027 M[subscript circled dot]. The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high conﬁdence, corresponding to a planetary radius of R[subscript p] = 2.53 [plus or minus] 0.18 R[subscript circled plus]. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 [plus or minus] 1.33 M[subscript circled plus] planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite conﬁrm the transit observed in the K2 photometry and provide a reﬁned ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.
Publisher's version/PDF
2015-02-10T00:00:00ZA coordinated X-ray and optical campaign of the nearest massive eclipsing binary, [delta] Orionis Aa. III. Analysis of optical photometric (MOST) and spectroscopic (ground based) variationsPablo, HerbertRichardson, Noel D.Moffat, Anthony F. J.Corcoran, MichaelShenar, TomerBenvenuto, OmarFuller, JimNaze, YaelHoffman, Jennifer L.Miroshnichenko, AnatolyGuenther, David B.http://library2.smu.ca:80/handle/01/268652017-04-12T12:41:53Z2015-08-20T00:00:00ZA coordinated X-ray and optical campaign of the nearest massive eclipsing binary, [delta] Orionis Aa. III. Analysis of optical photometric (MOST) and spectroscopic (ground based) variations
We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system [delta] Ori A, consisting of a binary O9.5II+early-B (Aa1 and Aa2) with P = 5.7 days, and a more distant tertiary (O9 IV P [greater than] 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
Publisher's version/PDF
2015-08-20T00:00:00ZThe discovery of the first “changing look” quasar: new insights into the physics and phenomenology of active galactic nucleiLaMassa, Stephanie M.Cales, SabrinaMoran, Edward C.Myers, Adam D.Richards, Gordon T.Eracleous, MichaelHeckman, Timothy M.Gallo, Luigi C.Urry, C. Meganhttp://library2.smu.ca:80/handle/01/268642017-04-03T23:59:24Z2015-02-20T00:00:00ZThe discovery of the first “changing look” quasar: new insights into the physics and phenomenology of active galactic nuclei
SDSS J015957.64+003310.5 is an X-ray selected, z = 0.31 active galactic nucleus (AGN) from the Stripe 82X survey that transitioned from a Type 1 quasar to a Type 1.9 AGN between 2000 and 2010. This is the most distant AGN, and first quasar, yet observed to have undergone such a dramatic change. We re-observed the source with the double spectrograph on the Palomar 5 m telescope in 2014 July and found that the spectrum is unchanged since 2010. From fitting the optical spectra, we find that the AGN flux dropped by a factor of 6 between 2000 and 2010 while the broad H[alpha] emission faded and broadened. Serendipitous X-ray observations caught the source in both the bright and dim state, showing a similar 2–10 keV flux diminution as the optical while lacking signatures of obscuration. The optical and X-ray changes coincide with g-band magnitude variations over multiple epochs of Stripe 82 observations. We demonstrate that variable absorption, as might be expected from the simplest AGN unification paradigm, does not explain the observed photometric or spectral properties. We interpret the changing state of J0159+0033 to be caused by dimming of the AGN continuum, reducing the supply of ionizing photons available to excite gas in the immediate vicinity around the black hole. J0159+0033 provides insight into the intermittency of black hole growth in quasars, as well as an unprecedented opportunity to study quasar physics (in the bright state) and the host galaxy (in the dim state), which has been impossible to do in a single sources [sic] until now.
Publisher's version/PDF
2015-02-20T00:00:00ZThe role of turbulence and magnetic fields in simulated filamentary structureKirk, HelenKlassen, MikhailPudritz, RalphPillsworth, Samanthahttp://library2.smu.ca:80/handle/01/268632017-03-30T15:57:18Z2015-04-01T00:00:00ZThe role of turbulence and magnetic fields in simulated filamentary structure
We use numerical simulations of turbulent cluster-forming regions to study the nature of dense filamentary structures in star formation. Using four hydrodynamic and magnetohydrodynamic simulations chosen to match observations, we identify filaments in the resulting column density maps and analyze their properties. We calculate the radial column density profiles of the filaments every 0.05 Myr and fit the profiles with the modified isothermal and pressure-confined isothermal cylinder models, finding reasonable fits for either model. The filaments formed in the simulations have similar radial column density profiles to those observed. Magnetic fields provide additional pressure support to the filaments, making “puffier” filaments less prone to fragmentation than in the pure hydrodynamic case, which continue to condense at a slower rate. In the higher density simulations, the filaments grow faster through the increased importance of gravity. Not all of the filaments identified in the simulations will evolve to form stars: some expand and disperse. Given these different filament evolutionary paths, the trends in bulk filament width as a function of time, magnetic field strength, or density are weak, and all cases are reasonably consistent with the finding of a constant filament width in different star-forming regions. In the simulations, the mean FWHM lies between 0.06 and 0.26 pc for all times and initial conditions, with most lying between 0.1 to 0.15 pc; the range in FWHMs is however, larger than seen in typical Herschel analyses. Finally, the filaments display a wealth of substructure similar to the recent discovery of filament bundles in Taurus.
Publisher's version/PDF
2015-04-01T00:00:00ZRadial stellar pulsation and three-dimensional convection. IV. Full amplitude three-dimensional solutionsGeroux, Christopher M.Deupree, Robert G. (Robert Gaston), 1946-http://library2.smu.ca:80/handle/01/268622017-03-22T15:41:34Z2015-02-10T00:00:00ZRadial stellar pulsation and three-dimensional convection. IV. Full amplitude three-dimensional solutions
Three-dimensional hydrodynamic simulations of full amplitude RR Lyrae stars have been computed for several models across the instability strip. The three-dimensional nature of the calculations allows convection to be treated without reference to a phenomenological approach such as the local mixing length theory. Specifically, the time-dependent interaction of large-scale eddies and radial pulsation is controlled by conservation laws, while the effects
of smaller convective eddies are simulated by an eddy viscosity model. The light amplitudes for these calculations are quite similar to those of our previous two-dimensional calculations in the middle of the instability strip, but somewhat lower near the red edge, the fundamental blue edge, and for the one first overtone model we computed. The time-dependent interaction between the radial pulsation and the convective energy transport is essentially the same in three dimensions as it is in two dimensions. There are some differences between the light curves of the two- and three-dimensional simulations, particularly during decreasing light. Reasons for the differences, both numerical and physical, are explored.
Publisher's version/PDF
2015-02-10T00:00:00ZProperties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxiesFoschini, L.Berton, M.Caccianiga, A.Ciroi, S.Cracco, V.Peterson, B. M.Angelakis, E.Braito, V.Fuhrmann, L.Gallo, Luigi C.http://library2.smu.ca:80/handle/01/268512017-03-10T19:48:38Z2015-03-01T00:00:00ZProperties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
We have conducted a multiwavelength survey of 42 radio loud narrow-line Seyfert 1 galaxies (RLNLS1s), selected by searching among all the known sources of this type and omitting those with steep radio spectra. We analyse data from radio frequencies to X-rays, and supplement these
with information available from online catalogues and the literature in order to cover the full electromagnetic spectrum. This is the largest known multiwavelength survey for this type of source. We detected 90% of the sources in X-rays and found 17% at [gamma] rays. Extreme variability at high energies was also found, down to timescales as short as hours. In some sources, dramatic spectral and flux changes suggest interplay between a relativistic jet and the accretion disk. The estimated masses of the central black holes are in the range ∼10[superscript 6−8] M[subscript circled dot], lower than those of blazars, while the accretion luminosities span a range from ∼0.01 to ∼0.49 times the Eddington limit, with an outlier at 0.003, similar to those of quasars. The distribution of the calculated jet power spans a range from ∼10[superscript 42.6] to ∼10[superscript 45.6] erg s[superscript −1], generally lower than quasars and BL Lac objects, but partially overlapping with the latter. Once normalised by the mass of the central black holes, the jet power of the three types of active galactic nuclei are consistent with each other, indicating that the jets are similar and the observational differences are due to scaling factors. Despite the observational differences, the central engine of RLNLS1s is apparently quite similar to that of blazars. The historical difficulties in finding radio-loud narrow-line Seyfert 1 galaxies might be due to their low power and to intermittent jet activity.
Publisher's version/PDF
2015-03-01T00:00:00ZReddenings of FGK supergiants and classical Cepheids from spectroscopic dataKovtyukh, V. V.Soubiran, C.Luck, R. E.Turner, David Gerald, 1945-Belik, S. I.Andrievsky, S. M.Chekhonadskikh, F. A.http://library2.smu.ca:80/handle/01/267342017-01-23T19:00:13Z2008-01-01T00:00:00ZReddenings of FGK supergiants and classical Cepheids from spectroscopic data
Accurate and homogeneous atmospheric parameters (T[subscript eff], log g, V[subscript t], [Fe/H]) are derived for 74 FGK non-variable supergiants from high-resolution, high signal-to-noise ratio, echelle spectra. Extremely high precision for the inferred effective temperatures (10–40 K) is achieved by using the line-depth ratio method. The new data are combined with atmospheric values for 164 classical Cepheids, observed at 675 different pulsation phases, taken from our previously published studies. The derived values are correlated with unreddened B − V colours compiled from the literature for the investigated stars in order to obtain an empirical relationship of the form (B − V)[subscript 0] = 57.984 − 10.3587(log T[subscript eff)[superscript 2] + 1.675 72(log T[subscript eff])[superscript 3] − 3.356 log g + 0.0321V[subscript t] + 0.2615[Fe/H] + 0.8833(log g)(log T[subscript eff]). The expression is used to estimate colour excesses E(B − V) for individual supergiants and classical Cepheids, with a precision of [plus or minus]0.05 mag for supergiants and Cepheids with n = 1–2 spectra, reaching [plus or minus]0.025 mag for Cepheids with n > 2 spectra, matching uncertainties
for the most sophisticated photometric techniques. The reddening scale is also a close match to the system of space reddenings for Cepheids. The application range is for spectral types F0–K0 and luminosity classes I and II.
Publisher's version/PDF
2008-01-01T00:00:00Z