And now for some real science.

https://arxiv.org/pdf/1807.00008

Type II Cepheids have been traditionally divided into three classes: BL Her, W Vir, and RV Tau stars. BL Her stars, with the shortest pulsation periods (1– 4 d), evolve from the horizontal branch to the asymptotic giant branch (AGB).

W Vir stars with intermediate periods (4–20 d) are thought to experience thermal pulses which result in blue loops into the instability strip region in the Hertzsprung-Russell (HR) diagram, however a convincing evolutionary model that would quantitatively describe this behavior still does not exist.

RV Tau variables with the longest periods (> 20 d) are post AGB stars, just prior to the expulsion of planetary nebulae.

peculiar W Vir stars are related to the so called binary evolution pulsators (BEPs) that are binary stars.

the number of type II Cepheids is much smaller than their classical siblings. Classical cephids form a pair of straight lines on the chart of luminosity vs log period. “Anomalous cephids” form a third line parallel to the first two. Type II cepheids line up in a fourth line parallel to the first three. The study also found two Cepheids (Ogle numbers 207 and 237) that are way out of position.

The interest for mollwollfumble is the post AGB stars that are just about to throw off their mass in a planetary nebula. We’ve never seen a new planetary nebula form in the past 100 years and this event ought to occur more often than supernovas.

The interest for mollwollfumble is the post AGB stars that are just about to throw off their mass in a planetary nebula. We’ve never seen a new planetary nebula form in the past 100 years and this event ought to occur more often than supernovas.

Are they as easily (relatively speaking) to detect as a supernovas

Here’s a HR chart showing lots of different types of variable stars including some (eg.flare stars) way off the instability strip.

mollwollfumble said:

And now for some real science.

https://arxiv.org/pdf/1807.00008

Type II Cepheids have been traditionally divided into three classes: BL Her, W Vir, and RV Tau stars. BL Her stars, with the shortest pulsation periods (1– 4 d), evolve from the horizontal branch to the asymptotic giant branch (AGB).

W Vir stars with intermediate periods (4–20 d) are thought to experience thermal pulses which result in blue loops into the instability strip region in the Hertzsprung-Russell (HR) diagram, however a convincing evolutionary model that would quantitatively describe this behavior still does not exist.

RV Tau variables with the longest periods (> 20 d) are post AGB stars, just prior to the expulsion of planetary nebulae.

peculiar W Vir stars are related to the so called binary evolution pulsators (BEPs) that are binary stars.

the number of type II Cepheids is much smaller than their classical siblings. Classical cephids form a pair of straight lines on the chart of luminosity vs log period. “Anomalous cephids” form a third line parallel to the first two. Type II cepheids line up in a fourth line parallel to the first three. The study also found two Cepheids (Ogle numbers 207 and 237) that are way out of position.

The interest for mollwollfumble is the post AGB stars that are just about to throw off their mass in a planetary nebula. We’ve never seen a new planetary nebula form in the past 100 years and this event ought to occur more often than supernovas.

LOL

Cymek said:

The interest for mollwollfumble is the post AGB stars that are just about to throw off their mass in a planetary nebula. We’ve never seen a new planetary nebula form in the past 100 years and this event ought to occur more often than supernovas.

Are they as easily (relatively speaking) to detect as a supernovas

Nowhere near as easy to detect. So far as I know, no-one is even sure if the event will be marked by a sucden brightening or sudden darkening.

mollwollfumble said:

And now for some real science.

https://arxiv.org/pdf/1807.00008

Type II Cepheids have been traditionally divided into three classes: BL Her, W Vir, and RV Tau stars. BL Her stars, with the shortest pulsation periods (1– 4 d), evolve from the horizontal branch to the asymptotic giant branch (AGB).

…

the number of type II Cepheids is much smaller than their classical siblings. Classical cephids form a pair of straight lines on the chart of luminosity vs log period. “Anomalous cephids” form a third line parallel to the first two. Type II cepheids line up in a fourth line parallel to the first three. The study also found two Cepheids (Ogle numbers 207 and 237) that are way out of position.

The interest for mollwollfumble is the post AGB stars that are just about to throw off their mass in a planetary nebula. We’ve never seen a new planetary nebula form in the past 100 years and this event ought to occur more often than supernovas.

Plot of period vs brightness. The four lines and two outliers. The small dots are classical cepheids, the middle sized dots are “anomalous cepheids” and the large dots are type !! cepheids.