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Extrasolar Visions II

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 Welcome back to Aldebaran (A)b?

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Edasich
dK star
dK star
Edasich


Number of posts : 2267
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

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PostSubject: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty14th May 2015, 4:01 am

Radial velocity pointing to planetary companion and stellar activity seem disentangled.

Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity

Quote :
We investigate the nature of the long-period radial velocity variations in Alpha Tau first reported over 20 years ago. We analyzed precise stellar radial velocity measurements for Alpha Tau spanning over 30 years. An examination of the Halpha and Ca II 8662 spectral lines, and Hipparcos photometry was also done to help discern the nature of the long-period radial velocity variations. Our radial velocity data show that the long-period, low amplitude radial velocity variations are long-lived and coherent. Furthermore, Halpha equivalent width measurements and Hipparcos photometry show no significant variations with this period. Another investigation of this star established that there was no variability in the spectral line shapes with the radial velocity period. An orbital solution results in a period of P = 628.96 +/- 0.90 d, eccentricity, e = 0.10 +/- 0.05, and a radial velocity amplitude, K = 142.1 +/- 7.2 m/s. Evolutionary tracks yield a stellar mass of 1.13 +/- 0.11 M_sun, which corresponds to a minimum companion mass of 6.47 +/- 0.53 M_Jup with an orbital semi-major axis of a = 1.46 +/- 0.27 AU. After removing the orbital motion of the companion, an additional period of ~ 520 d is found in the radial velocity data, but only in some time spans. A similar period is found in the variations in the equivalent width of Halpha and Ca II. Variations at one-third of this period are also found in the spectral line bisector measurements. The 520 d period is interpreted as the rotation modulation by stellar surface structure. Its presence, however, may not be long-lived, and it only appears in epochs of the radial velocity data separated by ∼ 10 years. This might be due to an activity cycle. The data presented here provide further evidence of a planetary companion to Alpha Tau, as well as activity-related radial velocity variations.

I say "Aldebaran Ab" accounting M dwarf companion B too.

*edit*

"Reloaded" to EPE:

http://exoplanet.eu/catalog/aldebaran_b/
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Lazarus
dF star
dF star



Number of posts : 3337
Registration date : 2008-06-12

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PostSubject: Re: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty28th February 2018, 5:21 pm

Farr et al. "Aldebaran b's temperate past uncovered in planet search data"
https://arxiv.org/abs/1802.09812

Updated determination of the Aldebaran system's properties, including a new asteroseismic mass determination for the star. It appears that Aldebaran b was in the habitable zone for (some of) the star's main sequence evolution.

There is also some interesting discussion of the Gamma Draconis problem.
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Sirius_Alpha
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Sirius_Alpha


Number of posts : 4319
Location : Earth
Registration date : 2008-04-06

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PostSubject: Re: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty24th March 2019, 8:39 pm

Whelp, ...

Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b
https://arxiv.org/abs/1903.09157

Quote :
Radial-velocity variations of the K giant star Aldebaran (α Tau) were first reported in the early 1990s. After subsequent analyses, the radial-velocity variability with a period of ∼629d has recently been interpreted as caused by a planet of several Jovian masses. We want to further investigate the hypothesis of an extrasolar planet around Aldebaran. We combine 165 new radial-velocity measurements from Lick Observatory with seven already published data sets comprising 373 radial-velocity measurements. We perform statistical analyses and investigate whether a Keplerian model properly fits the radial velocities. We also perform a dynamical stability analysis for a possible two-planet solution. As best Keplerian fit to the combined radial-velocity data we obtain an orbit for the hypothetical planet with a smaller period (P=607d) and a larger eccentricity (e=0.33±0.04) than the previously proposed one. However, the residual scatter around that fit is still large, with a standard deviation of 117ms−1. In 2006/2007, the statistical power of the ∼620d period showed a temporary but significant decrease. Plotting the growth of power in reverse chronological order reveals that a period around 620d is clearly present in the newest data but not in the data taken before ∼ 2006. Furthermore, an apparent phase shift between radial-velocity data and orbital solution is observable at certain times. A two-planet Keplerian fit matches the data considerably better than a single-planet solution, but poses severe dynamical stability issues. The radial-velocity data from Lick Observatory do not further support but in fact weaken the hypothesis of a substellar companion around Aldebaran. Oscillatory convective modes might be a plausible alternative explanation of the observed radial-velocity variations.

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Edasich
dK star
dK star
Edasich


Number of posts : 2267
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

Welcome back to Aldebaran (A)b? Empty
PostSubject: Re: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty26th March 2019, 5:55 pm

I think it shall return. It is not the first time that activity masquerades planets inducing to retraction and subsequent re-confirmation.
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Lazarus
dF star
dF star



Number of posts : 3337
Registration date : 2008-06-12

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PostSubject: Re: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty15th January 2020, 3:55 pm

An ongoing project studying oscillations in Aldebaran:

Beck et al. (2020) "The BRITE-SONG of Aldebaran -- Stellar Music in three voices"
https://arxiv.org/abs/2001.04912

Quote :
The long-periodic modulations previously reported in the literature are also present in the SONG dataset. Yet, it is too early to arrive at concrete conclusions on their origin. The long timebase and the high sampling rate of the radial-velocity measurements will help to decide if these variations are caused by a planetary companion, or by an unidentified physical process. We note that these variations are on different times scales than were found for secondary clump stars of the Hyades, which are likely to originate from rotational modulation (Beck et al. 2015; Arentoft et al. 2019).

It will be interesting to see what the final results will reveal.
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Edasich
dK star
dK star
Edasich


Number of posts : 2267
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

Welcome back to Aldebaran (A)b? Empty
PostSubject: Re: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty5th March 2023, 12:30 pm

Aldebaran b (actually c) is back?
http://exoplanet.eu/catalog/aldebaran_c/
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PostSubject: Re: Welcome back to Aldebaran (A)b?   Welcome back to Aldebaran (A)b? Empty

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