Kinematics and ages of Mira variables in the greater solar neighborhood

Wyatt, Stanley P.; Cahn, J. H.

doi:10.1086/161527

Cited by 35 publications

(33 citation statements)

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“…Mira variables follow a periodage relationship, with short periods corresponding to older stars (Wyatt & Cahn 1983), spanning a range of ages from ∼ 3 Gyr to globular cluster ages. Catchpole et al (2016) find that the younger ( 5 Gyr) Mira variables in the bulge at (l, b) = (±8 • , −7 • ) follow a clear bar structure, while the older ones are more spheroidal.…”

Section: Interpretation Of the Different Distributions Of Milky Way Bmentioning

confidence: 99%

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

Debattista

Ness

Gonzalez

et al. 2017

Monthly Notices of the Royal Astronomical Society

150

255

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We present a novel interpretation of the previously puzzling different behaviours of stellar populations of the Milky Way's bulge. We first show, by means of pure N -body simulations, that initially co-spatial stellar populations with different in-plane random motions separate when a bar forms. The radially cooler populations form a strong bar, and are vertically thin and peanut-shaped, while the hotter populations form a weaker bar and become a vertically thicker box. We demonstrate that it is the radial, not the vertical, velocity dispersion that dominates this evolution. Assuming that early stellar discs heat rapidly as they form, then both the in-plane and vertical random motions correlate with stellar age and chemistry, leading to different density distributions for metal-rich and metal-poor stars. We then use a high-resolution simulation, in which all stars form out of gas, to demonstrate that this is what happens. When we apply these results to the Milky Way we show that a very broad range of observed trends for ages, densities, kinematics and chemistries, that have been presented as evidence for contradictory paths to the formation of the bulge, are in fact consistent with a bulge which formed from a continuum of disc stellar populations which were kinematically separated by the bar. For the first time we are able to account for the bulge's main trends via a model in which the bulge formed largely in situ. Since the model is generic, we also predict the general appearance of stellar population maps of external edge-on galaxies.

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Section: Interpretation Of the Different Distributions Of Milky Way Bmentioning

confidence: 99%

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

Debattista

Ness

Gonzalez

et al. 2017

Monthly Notices of the Royal Astronomical Society

150

255

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“…In comparison with the stellar parameters of the P and M model series, RR Aql pulsates with a longer period of 394 days. The main sequence precursor mass of RR Aql is 1.2 ± 0.2 M/M (Wyatt & Cahn 1983), and its spectral type is M6e-M9 (Samus et al 2004), versus M5-M9 (P series) and M6-M9.5 (M series). For the purpose of the modeling effort conducted here, we can assume that the general properties of the P and M model series are also valid for a longer period variable such as RR Aql.…”

Section: Modeling Of Our Midi Datamentioning

confidence: 99%

Mid-infrared interferometric monitoring of evolved stars

Karovicova

Wittkowski²,

Boboltz³

et al. 2011

A&A

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Aims. We present a unique multi-epoch infrared interferometric study of the oxygen-rich Mira variable RR Aql in comparison to radiative transfer models of the dust shell. We investigate flux and visibility spectra at 8-13 μm with the aim of better understanding the pulsation mechanism and its connection to the dust condensation sequence and mass-loss process. Methods. We obtained 13 epochs of mid-infrared interferometry with the MIDI instrument at the VLTI between April 2004 and July 2007, covering minimum to pre-maximum pulsation phases (0.45-0.85) within four cycles. The data are modeled with a radiative transfer model of the dust shell where the central stellar intensity profile is described by a series of dust-free dynamic model atmospheres based on self-excited pulsation models. We examined two dust species, silicate and Al 2 O 3 grains. We performed model simulations using variations in model phase and dust shell parameters to investigate the expected variability of our mid-infrared photometric and interferometric data. Results. The observed visibility spectra do not show any indication of variations as a function of pulsation phase and cycle. The observed photometry spectra may indicate intracycle and cycle-to-cycle variations at the level of 1-2 standard deviations. The photometric and visibility spectra of RR Aql can be described well by the radiative transfer model of the dust shell that uses a dynamic model atmosphere describing the central source. The best-fitting model for our average pulsation phase of Φ V = 0.64 ± 0.15 includes the dynamic model atmosphere M21n (T model = 2550 K) with a photospheric angular diameter of θ Phot = 7.6 ± 0.6 mas, and a silicate dust shell with an optical depth of τ V = 2.8 ± 0.8, an inner radius of R in = 4.1 ± 0.7 R Phot , and a power-law index of the density distribution of p = 2.6 ± 0.3. The addition of an Al 2 O 3 dust shell did not improve the model fit. However, our model simulations indicate that the presence of an inner Al 2 O 3 dust shell with lower optical depth than for the silicate dust shell can not be excluded. The photospheric angular diameter corresponds to a radius of R phot = 520 +230 −140 R and an effective temperature of T eff ∼ 2420 ± 200 K. Our modeling simulations confirm that significant intracycle and cycle-to-cycle visibility variations are not expected for RR Aql at mid-infrared wavelengths within our uncertainties. Conclusions. We conclude that our RR Aql data can be described by a pulsating atmosphere surrounded by a silicate dust shell. The effects of the pulsation on the mid-infrared flux and visibility values are expected to be less than about 25% and 20%, respectively, and are too low to be detected within our measurement uncertainties.

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“…Compared to o Cet and R Leo, for which the P and M model series are designed, S Ori is a slightly cooler Mira variable (M6.5−M9.5 versus M5−M9/M6−M9.5, Samus et al 2004) with a longer period (420 d versus 332 d/310 d, Samus et al 2004), a larger main sequence precursor mass (1.3 M ver- Wyatt & Cahn 1983), and a larger radius (mean continuum photospheric radii roughly R ∼ 450 R versus ∼350 R ; based on BW05, Woodruff et al 2004;Fedele et al 2005). However, when scaled to variability phases between 0 and 1 and to the corresponding angular size on sky, the general model results are not expected to be dramatically different for S Ori compared to Mira stars, such as o Cet and R Leo.…”

Section: Atmosphere Model For S Orimentioning

confidence: 99%

The Mira variable S Orionis: relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs

Wittkowski

Boboltz

Ohnaka

et al. 2007

A&A

132

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Aims. We present the first multi-epoch study that includes concurrent mid-infrared and radio interferometry of an oxygen-rich Mira star. Results. The modeling of our MIDI data results in phase-dependent continuum photospheric angular diameters of 9.0 ± 0.3 mas (phase 0.42), 7.9 ± 0.1 mas (0.55), 9.7 ± 0.1 mas (1.16), and 9.5 ± 0.4 mas (1.27). The dust shell can best be modeled with Al 2 O 3 grains using phase-dependent inner boundary radii between 1.8 and 2.4 photospheric radii. The dust shell appears to be more compact with greater optical depth near visual minimum (τ V ∼ 2.5), and more extended with lower optical depth after visual maximum (τ V ∼ 1.5). The ratios of the 43.1 GHz/42.8 GHz SiO maser ring radii to the photospheric radii are 2.2 ± 0.3/2.1 ± 0.2 (phase 0.44), 2.4 ± 0.3/2.3 ± 0.4 (0.55), and 2.1 ± 0.3/1.9 ± 0.2 (1.15). The maser spots mark the region of the molecular atmospheric layers just beyond the steepest decrease in the mid-infrared model intensity profile. Their velocity structure indicates a radial gas expansion. Conclusions. S Ori shows significant phase-dependences of photospheric radii and dust shell parameters. Al 2 O 3 dust grains and SiO maser spots form at relatively small radii of ∼1.8−2.4 photospheric radii. Our results suggest increased mass loss and dust formation close to the surface near the minimum visual phase, when Al 2 O 3 dust grains are co-located with the molecular gas and the SiO maser shells, and a more expanded dust shell after visual maximum. Silicon does not appear to be bound in dust, as our data show no sign of silicate grains.

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Kinematics and ages of Mira variables in the greater solar neighborhood

Cited by 35 publications

References 0 publications

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

Mid-infrared interferometric monitoring of evolved stars

The Mira variable S Orionis: relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs

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