Multidata inverse problems and Bayesian solution methods in astronomy

Statistical analyses of measurements that can be described by statistical models are of essence in astronomy and in scientific inquiry in general. The sensitivity of such analyses, modelling approaches, and the consequent predictions, is sometimes highly dependent on the exact techniques applied, and improvements therein can result in significantly better understanding of the observed system of interest. Particularly, optimising the sensitivity of statistical techniques in detecting the faint signatures of low-mass planets orbiting the nearby stars is, together with improvements in instrumentation, essential in estimating the properties of the population of such planets, and in the race to detect Earth-analogs, i.e. planets that could support liquid water and, perhaps, life on their surfaces. We review the developments in Bayesian statistical techniques applicable to detections planets orbiting nearby stars and astronomical data analysis problems in general. We also discuss these techniques and demonstrate their usefulness by using various examples and detailed descriptions of the respective mathematics involved. We demonstrate the practical aspects of Bayesian statistical techniques by describing several algorithms and numerical techniques, as well as theoretical constructions, in the estimation of model parameters and in hypothesis testing. We also apply these algorithms to Doppler measurements of nearby stars to show how they can be used in practice to obtain as much information from the noisy data as possible. Bayesian statistical techniques are powerful tools in analysing and interpreting noisy data and should be preferred in practice whenever computational limitations are not too restrictive.Siirretty Doriast

Probabilities of exoplanet signals from posterior samplings

M. Tuomi and H. R. A. Jones, 'Probabilities of exoplanet signals from posterior samplings', Astronomy & Astrophysics, Vol 544, A166, (2012), the version of record is available online at DOI: 10.1051/0004-6361/201118114. © 2012 ESOEstimating the marginal likelihoods is an essential feature of model selection in the Bayesian context. It is especially crucial to have good estimates when assessing the number of planets orbiting stars when the models explain the noisy data with different numbers of Keplerian signals. We introduce a simple method for approximating the marginal likelihoods in practice when a statistically representative sample from the parameter posterior density is available. We use our truncated posterior mixture estimate to receive accurate model probabilities for models with differing number of Keplerian signals in radial velocity data. We test this estimate in simple scenarios to assess its accuracy and rate of convergence in practice when the corresponding estimates calculated using deviance information criterion can be applied to receive trustworthy results for reliable comparison. As a test case, we determine the posterior probability of a planet orbiting HD 3651 given Lick and Keck radial velocity data. The posterior mixture estimate appears to be a simple and an accurate way of calculating marginal integrals from posterior samples. We show, that it can be used to estimate the marginal integrals reliably in practice, given a suitable selection of parameter \lambda, that controls its accuracy and convergence rate. It is also more accurate than the one block Metropolis-Hastings estimate and can be used in any application because it is not based on assumptions on the nature of the posterior density nor the amount of data or parameters in the statistical model.Peer reviewe

A planetary system with gas giants and super-Earths around the nearby M dwarf GJ676A : Optimizing data analysis techniques for the detection of multi-planetary systems

G. Anglada-Escude and M. Tuomi, 'A planetary system via gas giants and super-Earths around the nearby M dwarf GJ 676A: Optimizing data analysis techniques for the detection of multi-planetary systems', Astronomy & Astrophysics, Vol. 548, A58 (2012). The version of record is available online at DOI: 10.1051/0004-6361/201219910 © ESO 2012 Published by EDP SciencesContext. Several M dwarfs are targets of systematical monitoring in searches for Doppler signals caused by low-mass exoplanet companions. As a result, an emerging population of high-multiplicity planetary systems around low-mass stars are being detected as well. Aims. We optimize classic data analysis methods and develop new ones to enhance the sensitivity towards lower amplitude planets in high-multiplicity systems. We apply these methods to the public HARPS observations of GJ≠676A, a nearby and relatively quiet M dwarf with one reported gas giant companion. Methods. We rederived Doppler measurements from public HARPS spectra using the recently developed template matching method (HARPS-TERRA software). We used refined versions of periodograms to assess the presence of additional low-mass companions. We also analysed the same dataset with Bayesian statistics tools and compared the performance of both approaches. Results. We confirm the already reported massive gas giant candidate and a long period trend in the Doppler measurements. In addition to that, we find very secure evidence in favour of two new candidates in close-in orbits and masses in the super-Earth mass regime. Also, the increased time-span of the observations allows the detection of curvature in the long-period trend. suggesting the presence of a massive outer companion whose nature is still unclear. Conclusions. Despite the increased sensitivity of our new periodogram tools, we find that Bayesian methods are significantly more sensitive and reliable in the early detection of candidate signals, but more work is needed to quantify their robustness against false positives. While hardware development is important in increasing the Doppler precision, development of data analysis techniques can help to reveal new results from existing data sets with significantly fewer resources. This new system holds the record of minimum-mass range (from Msini ~ 4.5 M⊕ to 5 Mjup) and period range (from P ~ 3.6 days to more than 10 years). Although all planet candidates are substantially more massive, it is the first exoplanetary system with a general architecture similar to our solar system. GJ 676A can be happily added to the family of high-multiplicity planetary systems around M dwarfs.Peer reviewe

Comment on "Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581"

This document is the Accepted Manuscript Version of the following article: Guillem Anglada-Escude and Mikko Tuomi, 'Comment on "Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581"', Science, Vol 347 (6226), 2015, the final, published version is available online at doi: 10.1126/science.1260796. © 2015 The American Association for the Advancement of Science. All rights reserved.Robertson et al. (Reports, 25 July 2014, p. 440) claimed that activity-induced variability is responsible for the Doppler signal of the proposed planet candidate GJ 581d. We point out that their analysis using periodograms of residual data is inappropriate and promotes inadequate tools. Because the claim challenges the viability of the method to detect exo-Earths, we encourage reanalysis and a deliberation on what the field-standard methods should be.Peer reviewe

Mikä on autovalmistajien halukkuus panostaa tuotekehitykseen ympäristöystävällisen teknologian käyttöönotossa

Ympäristöystävällisyys on tämän päivän suunta autoteollisuudessa. Mitä enemmän saadaan kilometrejä yhdellä tankillisella polttoainetta, sitä tehokkaampaa on moottoriteknologia. Tutkielmani tarkoitus on antaa lisää tietoa siitä miten paljon autoteollisuus on valmis panostamaan tutkimukseen ja kehitykseen ympäristöystävällisen teknologian edistämiseksi. Kyseessä eivät ole pelkästään autovalmistajan tuotot seuraavan kymmenen vuoden aikana, vaan ne ulottuvat vuosikymmenien päähän, joka johtuu autoteollisuuden öljyriippuvaisuudesta. 1/3 CO2 – päästöistä aiheutuu liikenteestä ja tulevaisuuden ympäristöystävällisen teknologian asemointi tehdään jo nyt. Tämän tutkimuksen teoriaosuus painottuu syihin miksi tehdään t&k:ta, millaiset kannustimet yritykselle luodaan, jotta yritys hyötyy siitä tulevaisuudessa ja esitetään tulevaisuudenkuvia t&k:sta. Empiirisessä osuudessa esitellään kolmen autovalmistajan ympäristöstrategiaa, moottoriteknologiaa ja tulevaisuuden näkymiä. Autovalmistajat on valittu sillä periaatteella, että ne poikkeavat mahdollisimman paljon toisistaan ja sen tarkoitus on luoda tutkimukseen kontrastia. Empiriaa täydentää myös kahden autoyrityksen edustajien haastattelu. Loppuyhteenvedossa ja analyysissa mainitaan, että ympäristönäkökulma autoilussa on tärkeä, koska on varmistettava tulevien sukupolvien autoilun tarpeet, puhdas elinympäristö sekä autoilusta johtuva hiilijalanjäljen koko. Kerrotaan myös millaisia tuloksia haastattelu autoyritysten edustajien kanssa antoi ja säästääkö ympäristöystävällinen autoilu rahaa.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Preoperative Risk Stratification of Endometrial Carcinoma : L1CAM as a Biomarker

Objective Preoperative or intraoperative risk assessment models are used to stratify patients with endometrial carcinoma to lymphadenectomy. Our aim was to determine whether preoperative analysis of L1 cell adhesion molecule (L1CAM) can improve risk assessment. Methods Immunohistochemical L1CAM staining was performed on endometrial biopsies of 241 patients and paired hysterectomy samples of 75 patients. Risk assessment models based on preoperative histologic type and grade, myometrial invasion, and/or tumor diameter and alternative models incorporating preoperative L1CAM were compared with regard to their capability of predicting lymph nodal or distant metastasis. Soluble L1 levels were measured by enzyme-linked immunosorbent assay in serum samples of 40 patients with endometrial carcinoma. Results The concordance rate between L1CAM staining results of preoperative and hysterectomy samples was moderate ( = 0.586, P <0.0001). Preoperative L1CAM expression was associated with nonendometrioid histology, lymph node involvement, advanced stage, and positive peritoneal cytology. Receiver operating characteristic curve analyses showed that L1CAM did not significantly improve risk stratification algorithms based on traditional risk factors. Intraoperative tumor diameter was an effective surrogate for myometrial invasion. There was no statistical difference between L1 serum levels of patients with an L1CAM-positive or L1CAM-negative endometrial carcinoma (P = 0.786). Conclusions L1 cell adhesion molecule expression in endometrial biopsy correlates with high-risk features of endometrial carcinoma but does not significantly improve risk stratification algorithms based on traditional factors. Soluble L1 detected in the serum of patients with endometrial carcinoma does not correlate with tumoral L1CAM expression.Peer reviewe

A new cold sub-Saturnian candidate planet orbiting GJ 221

Mikko Tuomi, 'A new cold sub-Saturnian candidate planet orbiting GJ 22', Monthly Notices of the Royal Astronomical Society, Letters, Vol 440: L1-L5, advanced access publication 11 February 2014. The version of record is available at doi: 10.1093/mnrasl/slu014 © 2014 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.We re-analyse the recently published HARPS and PFS velocities of the nearby K dwarf GJ 221 that have been reported to contain the signatures of two planets orbiting the star. Our goal is to see whether the earlier studies discussing the system fell victims of false negative detections. We perform the analyses by using an independent statistical method based on posterior samplings and model comparisons in the Bayesian framework that is known to be more sensitive to weak signals of low-mass planets. According to our analyses, we find strong evidence in favour of a third candidate planet in the system corresponding to a cold sub-Saturnian planet with an orbital period of 500 days and a minimum mass of 29 $M_{\oplus}$. Application of sub-optimal signal detection methods can leave low-amplitude signals undetected in radial velocity time-series. Our results suggest that the estimated statistical properties of low-mass planets can thus be biased because several signals corresponding to low-mass candidate planets may have gone unnoticed. This also suggests that the occurrence rates of such planets based on radial velocity surveys might be underestimated.Peer reviewe