HD 41248 - 2 sub neptunes with 7:5 resonance

http://arxiv.org/pdf/1304.7374.pdf

Ooh, an Fe/H = -0.4… that's maybe thick disk. It's getting on to a Tau Ceti-kinda metallicity, which is interesting because that's a lot of solid material in the protoplanetary disk that's missing compared to the Sun. Proportionately more gas means that Sub-Neptune is likely a correct term, though maybe not at that close to the star.

0.137 and 0.172 AU from host star with luminosity 0.7solar-so quite far away from significant mass loss zone
though still hot.First one b slightly less massive than uranus another c could be resemblance to gliese 1214 b

HARPS is taking our planets away. 

The HARPS search for southern extra-solar planets XXXV. The interesting case of HD41248: stellar activity, no planets?
http://arxiv.org/abs/1404.6135

Quote :

The search for planets orbiting metal-poor stars is of uttermost importance for our understanding of the planet formation models. However, no dedicated searches have been conducted so far for very low mass planets orbiting such objects. Only a few cases of low mass planets orbiting metal-poor stars are thus known. Amongst these, HD41248 is a metal-poor, solar-type star on which a resonant pair of super-Earth like planets has In the present paper we present a new planet search program that is using the HARPS spectrograph to search for Neptunes and Super-Earths orbiting a sample of metal-poor FGK dwarfs. We then present a detailed analysis of an additional 162 radial velocity measurements of HD41248, obtained within this program, with the goal of confirming the existence of the proposed planetary system. We analyzed the precise radial velocities, obtained with the HARPS spectrograph, together with several stellar activity diagnostics and line profile indicators. A careful analysis shows no evidence for the planetary system previously announced. One of the signals, with a period of about 25 days, is shown to be related to the rotational period of the star, and is clearly seen in some of the activity proxies. The remaining signal (P~18 days) could not be convincingly retrieved in the new data set. We discuss possible causes for the complex (evolving) signals observed in the data of HD41248, proposing that they may be explained by the appearance and disappearance of active regions on the surface of a star with strong differential rotation, or by a combination of the sparse data sampling and active region evolution.

 

Ouch, I suspect there's going to be a lot more of this kind of thing what with trying to detect small planets at the level where confusion with activity is a signifcant concern.

(The potential confusion between Jupiter analogues and stellar magnetic cycles will likely take a lot longer to work through...)

Evidence for planetary signals strengthened?

The curious case of HD41248. A pair of static signals buried behind red-noise
http://arxiv.org/abs/1406.3093

Quote :

Gaining a better understanding of the effects of stellar induced radial velocity noise is critical for the future of exoplanet studies, since the discovery of the lowest-mass planets using this method will require us to go below the intrinsic stellar noise limit. An interesting test case in this respect is that of the southern solar analogue HD41248. The radial velocity time series of this star has been proposed to contain either a pair of signals with periods of around 18 and 25 days, that could be due to a pair of resonant super-Earths, or a single and varying 25 day signal that could arise due to a complex interplay between differential rotation and modulated activity. In this letter we build-up more evidence for the former scenario, showing that the signals are still clearly significant even after more than 10 years of observations and they likely do not change in period, amplitude, or phase as a function of time, the hallmarks of static Doppler signals. We show that over the last two observing seasons this star was more intrinsically active and the noise reddened, highlighting why better noise models are needed to find the lowest amplitude signals, in particular models that consider noise correlations. This analysis shows that there is still sufficient evidence for the existence of two super-Earths on the edge of, or locked into, a 7:5 mean motion resonance orbiting HD41248.

Quote :

GJ581 provides another example of false positive radial velocity signals where a possible candidate planet (GJ581 d) was reported in Udry et al. (2007) with a period of 82 days, later shown to be a 1-year alias of another planet candidate period of 67 days (Mayor et al. 2009).

That's… not how aliases work.

Anyway, this is one definitely one of the most difficult cases so far. Considering the argument here, it would be best to get back to observing the star when it is less active.

Can you tell noise modelling is going to define radial velocity searches in the near future?

Also, it's important to not miss this:

Quote :

Finally, we also tested the signals as a function of wavelength using the reddest HARPS orders only. (see Anglada-Escudé & Butler (2012) and Tuomi et al. (2013) for details), and found no dependence of the signal properties or significances on wavelength. This indicates that neither of the signals show evidence for a dependency on wavelength, at least across the wavelength domain offered by HARPS. This would again argue against the origin of these signals being from magnetic activity cycles modulated by rotation.

This is arguably more convincing that whatever red noise models you can throw at the data. Wavelength dependency is an extraordinarily useful way to determine whether a radial velocity signal is stellar or gravitational. Indeed, I'm shocked to see that this is the first time it has been tested since… the HD 40307 paper?

As expected at least one of HD 41248 candidate exoplanets comes back to life:

Agatha: disentangling periodic signals from correlated noise in a periodogram framework

Quote :

Periodograms are used as a key significance assessment and visualisation tool to display the significant periodicities in unevenly sampled time series. We introduce a framework of periodograms, called "Agatha", to disentangle periodic signals from correlated noise and to solve the 2-dimensional model selection problem: signal dimension and noise model dimension. These periodograms are calculated by applying likelihood maximization and marginalization and combined in a self-consistent way. We compare Agatha with other periodograms for the detection of Keplerian signals in synthetic radial velocity data produced for the Radial Velocity Challenge as well as in radial velocity datasets of several Sun-like stars. In our tests we find Agatha is able to recover signals to the adopted detection limit of the radial velocity challenge. Applied to real radial velocity, we use Agatha to confirm previous analysis of CoRoT-7 and to find two new planet candidates with minimum masses of 15.1 M⊕ and 7.08 M⊕ orbiting HD177565 and HD41248, with periods of 44.5 d and 13.4 d, respectively. We find that Agatha outperforms other periodograms in terms of removing correlated noise and assessing the significances of signals with more robust metrics. Moreover, it can be used to select the optimal noise model and to test the consistency of signals in time. Agatha is intended to be flexible enough to be applied to time series analyses in other astronomical and scientific disciplines. Agatha is available at this http URL

Along with a new fellow too, HD 177565 b, a new exoplanet in Corona Australis.

So according to that paper, HD 41248 is another case where the originally-announced period turns out to be an alias.

And it's gone again...

Decoding the radial velocity variations of HD41248 with ESPRESSO
https://arxiv.org/abs/1911.11714

Quote :

Twenty-four years after the discoveries of the first exoplanets, the radial-velocity (RV) method is still one of the most productive techniques to detect and confirm exoplanets. But stellar magnetic activity can induce RV variations large enough to make it difficult to disentangle planet signals from the stellar noise. In this context, HD41248 is an interesting planet-host candidate, with RV observations plagued by activity-induced signals. We report on ESPRESSO observations of HD41248 and analyse them together with previous observations from HARPS with the goal of evaluating the presence of orbiting planets. Using different noise models within a general Bayesian framework designed for planet detection in RV data, we test the significance of the various signals present in the HD41248 dataset. We use Gaussian processes as well as a first-order moving average component to try to correct for activity-induced signals. At the same time, we analyse photometry from the TESS mission, searching for transits and rotational modulation in the light curve. The number of significantly detected Keplerian signals depends on the noise model employed, which can range from 0 with the Gaussian process model to 3 with a white noise model. We find that the Gaussian process alone can explain the RV data while allowing for the stellar rotation period and active region evolution timescale to be constrained. The rotation period estimated from the RVs agrees with the value determined from the TESS light curve. Based on the data that is currently available, we conclude that the RV variations of HD41248 can be explained by stellar activity (using the Gaussian process model) in line with the evidence from activity indicators and the TESS photometry.

So we're already seeing ESPRESSO results!

Quote :

This work presents, for the first time, radial velocities obtained with ESPRESSO. The data clearly show that the instrument is already delivering on the expected RV precision in its first semester of operations. The limited time span of our observations does not allow us to comment on the long-term RV stability but the gain in precision relative to current state-of-the-art spectrographs like HARPS is evident.

Nice to see that it seems to be doing well, hopefully many more results to come...