Category Archives: Publications

Kelt-21b: A hot Jupiter transiting the rapidly-rotating metal-poor late-A primary of a likely hierarchical triple system

We present the discovery of KELT-21b, a hot Jupiter transiting the V = 10.5 A8V star HD 332124. The planet has an orbital period of P = 3.6127647 ± 0.0000033 days and a radius of 1.586 RJ. We set an upper limit on the planetary mass of MP< 3.91 MJ at 3σ confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spin-orbit misalignment of λ =-5.6° . The star has Teff=7598 K, M=1.458 M☉ , R=1.638 R☉ , and vsini=146 km s-1, the highest projected rotation velocity of any star known to host a transiting hot Jupiter. The star also appears to be somewhat metal poor and α-enhanced, with Fe/H=-0.405 and [α/Fe] = 0.145 ± 0.053 these abundances are unusual, but not extraordinary, for a young star with thin-disk kinematics like KELT-21. High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1.″2 and with a combined contrast of 6.39 with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of ∼0.12 M☉ , a projected mutual separation of ∼20 au, and a projected separation of ∼500 au from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems.

Read more: Johnson et al. 2018, AJ, 2018, 155, 100

High Resolution Optical Spectroscopy of the Classical Nova V5668 Sgr Showing the Presence of Lithium

The classical nova (CN) V5668 Sgr was discovered on 2015 March 15.634 and initial optical spectra implied it was an Fe II-class CN. We obtained high resolution optical spectroscopy on 30 nights between 2015 April 3 and 2016 June 5 with the 2 x 8.4 m Large Binocular Telescope (LBT) and the 1.8 m Vatican Advanced Technology Telescope (VATT) using the Potsdam Echelle Polarimetric Spectroscopic Instrument (PEPSI). The spectra cover all or part of the 3830-9065 Å spectral region at a spectral resolution of up to 270,000 (1 km/s); the highest resolution currently available on any 8-10 m class telescope. The early spectra are dominated by emission lines of the Balmer and Paschen series of hydrogen, Fe II, Ca II, and Na I with P Cyg-type line profiles as well as emission lines of [O I]. Numerous interstellar lines and bands are readily apparent at high spectral resolution. The permitted line profiles show complex and dramatic variations in the multi-component P Cyg-type line profiles with time. We detect a weak blue-shifted absorption line at a velocity consistent with Li I 6708 Å when compared with the line profiles of Hβ, Fe II 5169 Å, and Na I D. This line is present in spectra obtained on 7 of 8 consecutive nights up to day 21 of the outburst; but absent on day 42 when it is evident that the ionization of the ejecta has significantly increased. The equivalent width of the line converted to a column density, and the resulting mass fraction, imply a significant enrichment of 7Li in the ejecta. 7Li is produced by the decay of unstable 7Be created during the thermonuclear runaway. The discovery of the resonance lines of 7Be II in the optical spectra of the recent CNe V339 Del, V2944 Oph, and V5668 Sgr by Tajitsu et al. (2016) and its subsequent decay to 7Li (half life of 53 days) suggests a significant enrichment of 7Li in the Galaxy from CNe is possible. Our observations of the Li I 6708 Å line in the early optical spectra of V5668 Sgr mark the second direct detection of Li in a CN following the detection of Li I in the early optical spectra of V1369 Cen by Izzo et al. (2015).

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Publication:  Wagner, R. Mark; Woodward, Charles E.; Starrfield, Sumner; Ilyin, Ilya; Strassmeier, Klaus
American Astronomical Society, AAS Meeting #231, id. 358.10

Posters presented at the 2nd LBT users meeting in Florence on June 20-23, 2017.

Lithium in the active sub-giant HD123351. A quantitative analysis with 3D and 1D model atmospheres using different observed spectra

Here we present a spectroscopic comparative analysis of the Li doublet region of HD 123351, an active sub-giant star of solar metallicity. We fit the Li profile in three observed spectra characterized by different qualities: two very-high resolution spectra (Gecko@CFHT, R=120 000, SNR=400 and PEPSI@LBT, R=150 000, SNR=663) and a high-resolution SOPHIE@OHP spectrum (R=40 000, SNR=300). We adopt a set of model atmospheres, both 3D and 1D, having different stellar parameters (T_{eff} and log g). The 3D models are taken from the CIFIST grid of COBOLD model atmospheres and departures from LTE are considered for the lithium components. For the blends other than the lithium in this wavelength region we adopt the linelist of Melendez et al. (2012, A&A, 543, 29). We find consistent results for all three observations and an overall good fit with the selected list of atomic and molecular lines, indicating a high 6Li content.

The presence of 6Li is not expected in cool stellar atmospheres. Its detection is of crucial importance for understanding mixing processes in stars and external lithium production mechanisms, possibly related to stellar activity or planetray accretion of 6Li-rich material.

Comparison of observed spectra of the Li doublet region of HD 123351 around 670.8 nm. The Gecko (blue dotted line), SOPHIE (red dashed line) and PEPSI (green dashed-dotted line) spectra are superimposed on the Solar flux atlas by Kurucz (2005) (black continuous line) for a comparison. The locations of the Li I components and the dominant blends attributed to Fe  and CN are also indicated.


Read more:  Mott, Steffen, Caffau, & Strassmeier 2017, MemSAI 88, 68


CoRoT photometry and STELLA spectroscopy of an eccentric, eclipsing, and spotted HgMn binary with sub-synchronized rotation

Context. We report the discovery and analysis of very narrow transits in the eccentric spectroscopic binary HSS 348 (IC 4756).
Aims: The aim is to characterize the full HSS 348 system.
Methods: We obtained high-precision CoRoT photometry over two long runs and multi-epoch high-resolution échelle spectroscopy and imaging with STELLA and first PEPSI spectra.
Results: HSS 348 is found to be an eccentric (e = 0.18) double-lined spectroscopic binary with a period of 12.47 d in which at least the primary component is a peculiar B star of the HgMn class. The orbital elements are such that the system undergoes a grazing eclipse with the primary in front but no secondary eclipse. The out-of-eclipse light variations show four nearly equidistant but unequal minima stable in shape and amplitude throughout our observations. Their individual photometric periods are all harmonics of the same fundamental period which happens to agree with the transit period to within the errors. We interpret the fundamental period to be the rotation period of at least one if not both stars due to surface inhomogeneities. Due to the non-zero eccentricity of the orbit the two components are rotating sub-synchronously.
Conclusions: It appears that HSS 348 is not a member of the IC 4756 cluster but a background B8+B8.5 binary system. Its sharp eclipses every 12.47 days just mimic a small-body transit but are in reality the grazing eclipses of a B-star binary and thus a classical false positive. The system seems to be pre-main sequence with the primary possibly just arrived on the ZAMS. The light curve with four unequal minima can be explained with four cool spots of different size equidistantly positioned in longitude. Our data do not allow to uniquely assign the spots to either of the two stars.

PEPSI spectrum showing a series of Mn II lines from the primary of HSS348 in IC4756.

Read more: Strassmeier et al. 2017, A&A 597, A55