Lauri Jetsu | University of Helsinki (original) (raw)

Papers by Lauri Jetsu

Research paper thumbnail of Say Hello to Algol's New Companion Candidates

The Astrophysical Journal, 2021

Constant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). T... more Constant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). These ephemerides based on the old data cannot accurately predict the observed future eclipse epochs (O). Predictability can be improved by removing linear or quadratic trends from the O − C data. Additional companions in an eclipsing binary system cause light-time travel effects that are observed as strictly periodic O − C changes. Recently, Hajdu et al. estimated that the probability of detecting the periods of two new companions from the O − C data is only 0.00005. We apply the new discrete chi-square method to 236 yr of O − C data of the eclipsing binary Algol (β Persei). We detect the tentative signals of at least five companion candidates having periods between 1.863 and 219.0 yr. The weakest one of these five signals does not reveal a "new" companion candidate, because its 680.4 ± 0.4 day signal period differs only 1.4σ from the well-known 679.85 ± 0.04 day orbital period of Algol C. We detect these same signals also from the first 226.2 yr of data, and they give an excellent prediction for the last 9.2 yr of our data. The orbital planes of Algol C and the new companion candidates are probably coplanar because no changes have been observed in Algol's eclipses. The 2.867 day orbital period has been constant since it was determined by Goodricke.

Research paper thumbnail of Discrete Chi-square Method for Detecting Many Signals

The Open Journal of Astrophysics

Research paper thumbnail of Algol as Horus in the Cairo Calendar: The Possible Means and the Motives of the Observations

Open Astronomy

An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck wit... more An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck with the period of 2.850 days. Previous astronomical, astrophysical and statistical analyses of CC support the idea that this was the period of the eclipsing binary Algol three millennia ago. However, next to nothing is known about who recorded Algol’s period into CC and especially how. Here, we show that the ancient Egyptian scribes had the possible means and the motives for such astronomical observations. Their principles of describing celestial phenomena as activity of gods reveal why Algol received the title of Horus.

Research paper thumbnail of Some Studies of Terrestrial Impact Cratering Rate

Open Astronomy

In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 M... more In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 Myr periodicity in the epochs of mass extinctions of species. Periodic comet showers from the Oort cloud seemed to cause catastrophic events linked to mass extinctions of species. Our first study revealed that the only significant detected periodicity is the “human signal” caused by the rounding of these data into integer numbers. The second study confirmed that the original 28.4 Myr periodicity detection was not significant. The third study revealed that the quality and the quantity of the currently available data would allow detection of real periodicity only if all impacts have been periodic, which cannot be the case. The detection of a periodic signal, if present, requires that more craters should be discovered and the accuracy of age estimates improved. If we sometimes will be able to find the difference between the craters caused by asteroid and comet impacts, the aperiodic componen...

Research paper thumbnail of Photometric variability of HD 82558

Research paper thumbnail of VizieR Online Data Catalog: Terrestrial impact cratering rate (Jetsu 1997)

Vizier Online Data Catalog, May 1, 1997

Research paper thumbnail of Terrestrial impact cratering rate (Jetsu 1997)

Research paper thumbnail of Surface Imaging of HD 199178: High Latitude Spot and Differential Rotation

ABSTRACT We present surface (Doppler) imaging temperature maps of the FK Comae-type star HD 19917... more ABSTRACT We present surface (Doppler) imaging temperature maps of the FK Comae-type star HD 199178 (V1794 Cyg). The maps have been calculated from high resolution spectra and simultaneous Johnson V-photometry obtained between 1994 and 1997. All maps reveal a high latitude spot, which is 1200-1600 K cooler than the mean surface temperature. The observed slightly flat bottomed absorption lines can be explained by antisolar surface differential rotation. The presence of differential rotation is supported by the variations in the photometric rotation period.

Research paper thumbnail of Active longitudes of $ sigma$ geminorum:another "flip-flop"?

Research paper thumbnail of A Decade of Photometry of Lq-Hydrae

Astronomy and Astrophysics, Aug 30, 1993

Research paper thumbnail of Active longitudes of sigma Gem: another

Proceedings of the International Astronomical Union, 1995

Research paper thumbnail of The active longitudes of $ lambda$ Andromedae, $ sigma$ Geminorum, II Pegasi and V711 Tauri

Research paper thumbnail of Uvby-photometry of AB Doradus

Astronomy and Astrophysics Supplement Series, Oct 30, 1990

Research paper thumbnail of Period changes of AR Lacertae between 1900 and 1989

Research paper thumbnail of Spurious periods in the terrestrial impact crater record

Astronomy and Astrophysics

We present a simple solution to the controversy over periodicity in the ages of terrestrial impac... more We present a simple solution to the controversy over periodicity in the ages of terrestrial impact craters and the epochs of mass extinctions of species. The first evidence for a 28.4 million year cycle in catastrophic impacts on Earth was presented in 1984. Our re-examination of this earlier Fourier power spectrum analysis reveals that the rounding of the impact crater data distorted the Monte Carlo significance estimates obtained for this cycle. This conclusion is confirmed by theoretical significance estimates with the Fourier analysis, as well as by both theoretical and Monte Carlo significance estimates with the Rayleigh method. We also apply other time series analysis methods to six subsamples of the currently available more extensive impact crater record and one sample of mass extinction epochs. This analysis reveals the spurious ``human-signal'' induced by rounding. We demonstrate how the data rounding interferes with periodicity analysis and enhances artificial peri...

Research paper thumbnail of Some Studies of Terrestrial Impact Cratering Rate

In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 M... more In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 Myr periodicity in the epochs of mass extinctions of species. Periodic comet showers from the Oort cloud seemed to cause catastrophic events linked to mass extinctions of species. Our first study revealed that the only significant detected periodicity is the ``human signal'' caused by the rounding of these data into integer numbers. The second study confirmed that the original 28.4 Myr periodicity detection was not significant. The third study revealed that the quality and the quantity of the currently available data would allow detection of real periodicity only if all impacts have been periodic, which cannot be the case. The detection of a periodic signal, if present, requires that more craters should be discovered and the accuracy of age estimates improved. If we sometimes will be able to find the difference between the craters caused by asteroid and comet impacts, the aperiodi...

Research paper thumbnail of Analysing the active longitudes of the young solar analogue HD 116956 using Bayesian statistics

Aims: In this study, we aim at investigating the properties of the active longitude system of the... more Aims: In this study, we aim at investigating the properties of the active longitude system of the young solar analogue HD 116956 in detail, especially concentrating on determining the rotation period of the spot-generating mechanism with respect to the photometric rotation period of the star itself. Because the nonparametric approach, like the Kuiper method, can only give the period of active longitudes, we formulate a new method that can determine the parameters the active longitude distribution uniquely. Methods: For this purpose, we have developed an analysis method, based on Bayesian statistics using Markov chain Monte Carlo, presented in this manuscript. One of the advantages of this method is that an estimate of the active longitude system rotation period, as well as the parameters of the shape and location of the active longitudes together with their respective error estimates. This allows us to compare the active longitude and mean photospheric rotation periods of the star. ...

Research paper thumbnail of The variations of the Hα line of HD199178

Lecture Notes in Physics, 1991

Research paper thumbnail of The spot activity of FK Comae Berenices

Lecture Notes in Physics, 1991

Research paper thumbnail of Is the longitudinal distribution of solar flares nonuniform?

Two methods of searching for periodicity in weighted time point series are applied to earlier maj... more Two methods of searching for periodicity in weighted time point series are applied to earlier major solar flare data during three decades (1956{1985). The results of this analysis are tested against new solar flare data during the four years 1989{1993. Active longitudes rotating with a constant synodic period of 22:d0690:d012 could explain the complete data set over both hemispheres. The nonuniform distribution of the flare activity with this period displays two active longitudes separated by 180, but also shows other detailed features. No signicant periodicity is detected on the southern solar hemi- sphere, whereas active zones rotating with a constant synodic period of 26:d722 0:d015 are present in the earlier and new data on the northern hemisphere. The main peculiarity is that twohighlysignicantperiodicities(22:d07/26:d72)aredetected in the same data. The phenomena detected are interpreted as a signature of a long{lived nonaxisymmetric component of the solar magnetic eld below t...

Research paper thumbnail of Say Hello to Algol's New Companion Candidates

The Astrophysical Journal, 2021

Constant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). T... more Constant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). These ephemerides based on the old data cannot accurately predict the observed future eclipse epochs (O). Predictability can be improved by removing linear or quadratic trends from the O − C data. Additional companions in an eclipsing binary system cause light-time travel effects that are observed as strictly periodic O − C changes. Recently, Hajdu et al. estimated that the probability of detecting the periods of two new companions from the O − C data is only 0.00005. We apply the new discrete chi-square method to 236 yr of O − C data of the eclipsing binary Algol (β Persei). We detect the tentative signals of at least five companion candidates having periods between 1.863 and 219.0 yr. The weakest one of these five signals does not reveal a "new" companion candidate, because its 680.4 ± 0.4 day signal period differs only 1.4σ from the well-known 679.85 ± 0.04 day orbital period of Algol C. We detect these same signals also from the first 226.2 yr of data, and they give an excellent prediction for the last 9.2 yr of our data. The orbital planes of Algol C and the new companion candidates are probably coplanar because no changes have been observed in Algol's eclipses. The 2.867 day orbital period has been constant since it was determined by Goodricke.

Research paper thumbnail of Discrete Chi-square Method for Detecting Many Signals

The Open Journal of Astrophysics

Research paper thumbnail of Algol as Horus in the Cairo Calendar: The Possible Means and the Motives of the Observations

Open Astronomy

An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck wit... more An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck with the period of 2.850 days. Previous astronomical, astrophysical and statistical analyses of CC support the idea that this was the period of the eclipsing binary Algol three millennia ago. However, next to nothing is known about who recorded Algol’s period into CC and especially how. Here, we show that the ancient Egyptian scribes had the possible means and the motives for such astronomical observations. Their principles of describing celestial phenomena as activity of gods reveal why Algol received the title of Horus.

Research paper thumbnail of Some Studies of Terrestrial Impact Cratering Rate

Open Astronomy

In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 M... more In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 Myr periodicity in the epochs of mass extinctions of species. Periodic comet showers from the Oort cloud seemed to cause catastrophic events linked to mass extinctions of species. Our first study revealed that the only significant detected periodicity is the “human signal” caused by the rounding of these data into integer numbers. The second study confirmed that the original 28.4 Myr periodicity detection was not significant. The third study revealed that the quality and the quantity of the currently available data would allow detection of real periodicity only if all impacts have been periodic, which cannot be the case. The detection of a periodic signal, if present, requires that more craters should be discovered and the accuracy of age estimates improved. If we sometimes will be able to find the difference between the craters caused by asteroid and comet impacts, the aperiodic componen...

Research paper thumbnail of Photometric variability of HD 82558

Research paper thumbnail of VizieR Online Data Catalog: Terrestrial impact cratering rate (Jetsu 1997)

Vizier Online Data Catalog, May 1, 1997

Research paper thumbnail of Terrestrial impact cratering rate (Jetsu 1997)

Research paper thumbnail of Surface Imaging of HD 199178: High Latitude Spot and Differential Rotation

ABSTRACT We present surface (Doppler) imaging temperature maps of the FK Comae-type star HD 19917... more ABSTRACT We present surface (Doppler) imaging temperature maps of the FK Comae-type star HD 199178 (V1794 Cyg). The maps have been calculated from high resolution spectra and simultaneous Johnson V-photometry obtained between 1994 and 1997. All maps reveal a high latitude spot, which is 1200-1600 K cooler than the mean surface temperature. The observed slightly flat bottomed absorption lines can be explained by antisolar surface differential rotation. The presence of differential rotation is supported by the variations in the photometric rotation period.

Research paper thumbnail of Active longitudes of $ sigma$ geminorum:another "flip-flop"?

Research paper thumbnail of A Decade of Photometry of Lq-Hydrae

Astronomy and Astrophysics, Aug 30, 1993

Research paper thumbnail of Active longitudes of sigma Gem: another

Proceedings of the International Astronomical Union, 1995

Research paper thumbnail of The active longitudes of $ lambda$ Andromedae, $ sigma$ Geminorum, II Pegasi and V711 Tauri

Research paper thumbnail of Uvby-photometry of AB Doradus

Astronomy and Astrophysics Supplement Series, Oct 30, 1990

Research paper thumbnail of Period changes of AR Lacertae between 1900 and 1989

Research paper thumbnail of Spurious periods in the terrestrial impact crater record

Astronomy and Astrophysics

We present a simple solution to the controversy over periodicity in the ages of terrestrial impac... more We present a simple solution to the controversy over periodicity in the ages of terrestrial impact craters and the epochs of mass extinctions of species. The first evidence for a 28.4 million year cycle in catastrophic impacts on Earth was presented in 1984. Our re-examination of this earlier Fourier power spectrum analysis reveals that the rounding of the impact crater data distorted the Monte Carlo significance estimates obtained for this cycle. This conclusion is confirmed by theoretical significance estimates with the Fourier analysis, as well as by both theoretical and Monte Carlo significance estimates with the Rayleigh method. We also apply other time series analysis methods to six subsamples of the currently available more extensive impact crater record and one sample of mass extinction epochs. This analysis reveals the spurious ``human-signal'' induced by rounding. We demonstrate how the data rounding interferes with periodicity analysis and enhances artificial peri...

Research paper thumbnail of Some Studies of Terrestrial Impact Cratering Rate

In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 M... more In 1984, a 28.4 Myr periodicity was detected in the ages of terrestrial impact craters and a 26 Myr periodicity in the epochs of mass extinctions of species. Periodic comet showers from the Oort cloud seemed to cause catastrophic events linked to mass extinctions of species. Our first study revealed that the only significant detected periodicity is the ``human signal'' caused by the rounding of these data into integer numbers. The second study confirmed that the original 28.4 Myr periodicity detection was not significant. The third study revealed that the quality and the quantity of the currently available data would allow detection of real periodicity only if all impacts have been periodic, which cannot be the case. The detection of a periodic signal, if present, requires that more craters should be discovered and the accuracy of age estimates improved. If we sometimes will be able to find the difference between the craters caused by asteroid and comet impacts, the aperiodi...

Research paper thumbnail of Analysing the active longitudes of the young solar analogue HD 116956 using Bayesian statistics

Aims: In this study, we aim at investigating the properties of the active longitude system of the... more Aims: In this study, we aim at investigating the properties of the active longitude system of the young solar analogue HD 116956 in detail, especially concentrating on determining the rotation period of the spot-generating mechanism with respect to the photometric rotation period of the star itself. Because the nonparametric approach, like the Kuiper method, can only give the period of active longitudes, we formulate a new method that can determine the parameters the active longitude distribution uniquely. Methods: For this purpose, we have developed an analysis method, based on Bayesian statistics using Markov chain Monte Carlo, presented in this manuscript. One of the advantages of this method is that an estimate of the active longitude system rotation period, as well as the parameters of the shape and location of the active longitudes together with their respective error estimates. This allows us to compare the active longitude and mean photospheric rotation periods of the star. ...

Research paper thumbnail of The variations of the Hα line of HD199178

Lecture Notes in Physics, 1991

Research paper thumbnail of The spot activity of FK Comae Berenices

Lecture Notes in Physics, 1991

Research paper thumbnail of Is the longitudinal distribution of solar flares nonuniform?

Two methods of searching for periodicity in weighted time point series are applied to earlier maj... more Two methods of searching for periodicity in weighted time point series are applied to earlier major solar flare data during three decades (1956{1985). The results of this analysis are tested against new solar flare data during the four years 1989{1993. Active longitudes rotating with a constant synodic period of 22:d0690:d012 could explain the complete data set over both hemispheres. The nonuniform distribution of the flare activity with this period displays two active longitudes separated by 180, but also shows other detailed features. No signicant periodicity is detected on the southern solar hemi- sphere, whereas active zones rotating with a constant synodic period of 26:d722 0:d015 are present in the earlier and new data on the northern hemisphere. The main peculiarity is that twohighlysignicantperiodicities(22:d07/26:d72)aredetected in the same data. The phenomena detected are interpreted as a signature of a long{lived nonaxisymmetric component of the solar magnetic eld below t...