April 28th, 2020

Jenab6

Racial Differences in Infection Rates for Sexually Transmitted Diseases

While being only 13% of the US population in 2005, blacks accounted for half of the AIDS cases diagnosed in the country that year. The HIV infection rate for heterosexual black men was about 14 times the rate for heterosexual white men. The infection rate for black women was 23 times higher than the infection rate for white women.

Also, 41% of men and 64% of women living with HIV/AIDS were black.

Between 2001 and 2004, 61% of people under age 25 diagnosed with AIDS were black.

In 2006, the infection rate for gonorrhea was 18 times higher for blacks than for whites. The group with the highest rate of gonorrhea infection was black females aged 15-19. When considering all ages, black males had a per capita infection rate for gonorrhea 25 times higher than that for white men, and black women had a rate 14 times higher than white women had.

In 2006, the per capita infection rate for chlamydia was 8 times higher among blacks than among whites. The rate among black males was about 12 times that for white men.

Of all cases of syphilis reported to the CDC in 2006, 43% were blacks. The rate of syphilis infections in black females was 16 times higher than in white women. The rate of syphilis infection among black males was five times higher than that of white men. The rate of congenital syphilis among black babies was 15 times higher than the corresponding rate among white babies.

In general, blacks are 3 times more likely than whites to have herpes.

Half of all black girls aged 14-19 have, or have had, at least one sexually transmitted disease.
Jenab6

Published value for physical parameters for objects in star Kepler-1649's system are wrong

Reference to the EXOKyoto pages at
http://www.exoplanetkyoto.org/exohtml/Kepler-1649.html
http://www.exoplanetkyoto.org/exohtml/Kepler-1649_b.html
http://www.exoplanetkyoto.org/exohtml/Kepler-1649_c.html

Statement on these pages: "The host star Kepler-1649 has apparent magnitude of +16.7, with absolute magnitude of +25.0."

Impossible. The star Kepler-1649 is 301.5 light years away (parallax 10.8187 mas) from Earth. This is farther than the standard distance of 10 parsecs, or 32.6156 light-years. The absolute magnitude will therefore be numerically less than the apparent magnitude, not greater. The distance modulus is

m − M = 5 log( dLY / 3.261563777 ) − 5

We can find the absolute magnitude on the assumption that the value for the apparent magnitude is correct.

dLY = 301.5
m = +16.7
m − M = 4.8293
M = +11.87

If these magnitudes are for the visual band, then the bolometric correction will be about −2.3, and the bolometric absolute magnitude will be about +9.57. Indeed, the greatest possible bolometric absolute magnitude (i.e. the lowest possible luminosity) for a red dwarf star, having about 0.075 M☉, is something like +14.6.

The official estimate for the mass of Kepler-1649 is 0.219 M☉, but I think that the correct value is somewhere between 0.236 M☉ and 0.247 M☉.

For example of my reasons, notice that the measured orbital period of exoplanet b is 8.68909 days and the estimated semimajor axis of its orbit is 0.0514. An application of Kepler's third law gives about 0.240 M☉ as the mass of star Kepler-1649.

A table of average stellar parameters for the main sequence is published by the University of Rochester, and it can be found at

https://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt

I have programmed my HP Prime calculator with a curve-fit to the data in that table. In the program, the user inputs the mass of the star, and everything else is calculated using that curve fit. It is possible to back out estimates of a star's mass by matching some other parameter, such as effective temperature or radius.

Of course, stars differ in their compositions and this has the effect of making real stars deviate from the average values of their parameters. But using the data for the "average" star we can still make good guesses.

Backtracking from an observed surface temperature of 3240K, I get an estimated mass of 0.247 M☉ for star Kepler-1649. Backtracking from an observed radius of 0.252 R☉, I get an estimated mass of 0.236 M☉ for star Kepler-1649. And, in addition, there is the value of 0.240 M☉ that comes from the analysis of the orbit of exoplanet b.

So you can see why I believe that the officially estimated mass (0.219 M☉) for star Kepler-1649 is too low.

Although the EXOKyoto page for exoplanet c does not indicate any radius for the orbit, elsewhere the orbital radius is estimated at 0.0649 AU, and the observed period is 19.5352551 days. However, there is a problem with that estimate for the orbital radius because it leads to a far-too-low estimated mass for star Kepler-1649 of only 0.0956 M☉.

Therefore, exoplanet c is probably farther away than has been estimated. If we assume that the star has a mass of 0.236 M☉, then the semimajor axis of the orbit of exoplanet c is 0.0882 AU. On the other hand, if the official estimate of 0.219 M☉ is correct for star Kepler-1649, then the semimajor axis of the orbit of exoplanet c is 0.0856 AU.

Probably the planets that orbit this star will be early targets for exploration or colonization starships sent by the Solar System Empire in the 23rd century, so we should endeavor to post our preliminary data as well as we can.


The discovery paper for Kepler-1649c can be found at this link.

https://iopscience.iop.org/article/10.3847/2041-8213/ab84e5

It cites a reasonable value for the orbital radius of this exoplanet, and so it is not the source of the incorrect value that is being presented elsewhere.

It gives these numbers:

Mass of star Kepler-1649 is 0.1977 ± 0.0051 solar masses.
Orbital period of planet Kepler-1649c is 19.53527 ± 0.00010 days.

So the orbital distance of Kepler-1649c is about 0.08270 AU, which is close to what I had estimated earlier (0.0882 AU or 0.0856 AU).

The "official" mass for star Kepler-1649 of 0.219 solar masses is the result of averaging the values for the mass that was presented in the paper linked above, with another value that had been previously measured using an earlier analysis of the orbit of exoplanet b.

The discovery paper did not present any off values for the orbital radius of exoplanet c. The incorrect values that I've seen elsewhere probably arise from someone making a typo and not noticing it in time, and then everyone downstream just copied it without checking.