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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 A visual band light curve for V752 Centauri, plotted from data presented by Sisteró and Castore de Sisteró (1973)[1] | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Centaurus |
| Right ascension | 11h 42m 48.08s[2] |
| Declination | −35° 48′ 57.5″[2] |
| Apparent magnitude (V) | 9.10 – 9.66[3] |
| Characteristics | |
| Evolutionary stage | F7/G0(V)[4] |
| Variable type | W UMa[5] |
| Astrometry | |
| Proper motion (μ) | RA: −52.175[2] mas/yr Dec.: −24.364[2] mas/yr |
| Parallax (π) | 7.9641±0.0495 mas[2] |
| Distance | 410 ± 3 ly (125.6 ± 0.8 pc) |
| Absolute magnitude (MV) | 4.00 ± 0.34[6] |
| Orbit | |
| Period (P) | 0.37023198 days[7] |
| Semi-major axis (a) | 2.59 ± 0.05 R☉[7] |
| Inclination (i) | 82.07 ± 0.06[7]° |
| Semi-amplitude (K1) (primary) | 83.2±5.7[8] km/s |
| Semi-amplitude (K2) (secondary) | 267.2±6.9[8] km/s |
| Details | |
| Age | 3.84[9] Gyr |
| Primary | |
| Mass | 1.31 ± 0.07[7] M☉ |
| Radius | 1.30 ± 0.02[7] R☉ |
| Luminosity | 2.00 ± 0.07}[7] L☉ |
| Temperature | 5,955 ± 77[5] K |
| Secondary | |
| Mass | 0.39 ± 0.02[7] M☉ |
| Radius | 0.77 ± 0.01[7] R☉ |
| Luminosity | 0.75 ± 0.03[7] L☉ |
| Temperature | 6,221 ± 81[5] K |
| Other designations | |
| V752 Cen, CD−35°7392, HD 101799, HIP 57129, SAO 202729[10] | |
| Database references | |
| SIMBAD | data |
V752 Centauri (HD 101799) is multiple star system[11] and variable star in the constellation of Centaurus. An eclipsing binary, its apparent magnitude has a maximum of 9.10, dimming to 9.66 during primary eclipse and 9.61 during secondary eclipse.[3] Its variability was discovered by Howard Bond in 1970.[12] From parallax measurements by the Gaia spacecraft, the system is located at a distance of 410 light-years (125.6 parsecs) from Earth.[2]
V752 Centauri is a contact binary of the W Ursae Majoris type, composed of two F-type stars with a combined spectral type of F7/G0(V).[4] Individually, the components have been classified as F8 + F5,[8] and F8 + F7.5.[13] With effective temperatures of 5,955 and 6,221 K,[5] the system is classified as a W Ursae Majoris variable of subtype W, where the secondary star is hotter than the primary; for this reason, the primary eclipses are caused by the occultation of the secondary star.[8][5] The system has an orbital period of only 0.3702 days and a separation of 2.59 solar radii. The orbit is inclined by 82° in relation to the plane of the sky.[7]
The combination of photometric and spectroscopic data have allowed the direct determination of the parameters of the stars. The primary component has a mass of 1.31 times the solar mass, radius of 1.30 times the solar radius and a luminosity double that of the Sun. The secondary has only 0.39 times the solar mass, 0.77 times the solar radius, and 0.75 times the solar luminosity.[7] Since the stars are in contact, there is considerable mass transfer from the secondary to the primary. It is estimated that the secondary star was initially the more massive star, with 1.76 times the solar mass, while the primary had an initial mass of 0.84 time the solar mass.[9] The system's age is estimated at 3.8 billion years.[9] All contact binary stars are expected to eventually merge into a single, fast-rotating star.[14]
The system's spectrum shows the spectral lines of a third star, which seems to be a K-type main sequence star. This third star is itself a spectroscopic binary with a period of 5.147 days, with a small companion that is probably an M-type red dwarf. The V752 Centauri system is thus composed of four stars, with two binary pairs that orbit each other.[11] Most contact binary stars have one or more distant companions, and were possibly formed by angular momentum loss due to gravitational interactions with these companion stars.[15][7]
The light curve analysis of V752 Centauri reveals that between 1970 and 2000, the orbital period of the eclipsing binary remained approximately constant, indicating there was no significant mass transfer. Around the year 2000, the period abruptly increased, possibly accompanied by a slightly dimmer primary eclipse.[16] Since then, the period has been increasing at a rate of 0.044 seconds per year, which is caused by mass transfer from the less massive star to the more massive one at a rate of 2.52×10−7 M☉ per year. This period change and the beginning of the mass transfer phase were possibly caused by interactions with the companion binary star.[7]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
V752 Centauri (HD 101799) is multiple star system and variable star in the constellation of Centaurus. An eclipsing binary, its apparent magnitude has a maximum of 9.10, dimming to 9.66 during primary eclipse and 9.61 during secondary eclipse. Its variability was discovered by Howard Bond in 1970. From parallax measurements by the Gaia spacecraft, the system is located at a distance of 410 light-years (125.6 parsecs) from Earth. V752 Centauri is a contact binary of the W Ursae Majoris type, composed of two F-type stars with a combined spectral type of F7/G0(V). Individually, the components have been classified as F8 + F5, and F8 + F7.5. With effective temperatures of 5,955 and 6,221 K, the system is classified as a W Ursae Majoris variable of subtype W, where the secondary star is hotter than the primary; for this reason, the primary eclipses are caused by the occultation of the secondary star. The system has an orbital period of only 0.3702 days and a separation of 2.59 solar radii. The orbit is inclined by 82° in relation to the plane of the sky. The combination of photometric and spectroscopic data have allowed the direct determination of the parameters of the stars. The primary component has a mass of 1.31 times the solar mass, radius of 1.30 times the solar radius and a luminosity double that of the Sun. The secondary has only 0.39 times the solar mass, 0.77 times the solar radius, and 0.75 times the solar luminosity. Since the stars are in contact, there is considerable mass transfer from the secondary to the primary. It is estimated that the secondary star was initially the more massive star, with 1.76 times the solar mass, while the primary had an initial mass of 0.84 time the solar mass. The system's age is estimated at 3.8 billion years. All contact binary stars are expected to eventually merge into a single, fast-rotating star. The system's spectrum shows the spectral lines of a third star, which seems to be a K-type main sequence star. This third star is itself a spectroscopic binary with a period of 5.147 days, with a small companion that is probably an M-type red dwarf. The V752 Centauri system is thus composed of four stars, with two binary pairs that orbit each other. Most contact binary stars have one or more distant companions, and were possibly formed by angular momentum loss due to gravitational interactions with these companion stars. The light curve analysis of V752 Centauri reveals that between 1970 and 2000, the orbital period of the eclipsing binary remained approximately constant, indicating there was no significant mass transfer. Around the year 2000, the period abruptly increased, possibly accompanied by a slightly dimmer primary eclipse. Since then, the period has been increasing at a rate of 0.044 seconds per year, which is caused by mass transfer from the less massive star to the more massive one at a rate of 2.52×10−7 M☉ per year. This period change and the beginning of the mass transfer phase were possibly caused by interactions with the companion binary star.
Tau Centauri is a solitary star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from τ Centauri, and abbreviated Tau Cen or τ Cen. This star is visible to the naked eye with an apparent visual magnitude of +3.86. The distance to this star, based upon an annual parallax shift of 24.3 mas, is 131 light years. It makes a star system with Gamma Centauri at 98% probability, both separated by 1.7 ly (0.53 pc). This is an A-type star with stellar classifications of A0 V or A1 IVnn, indicating it may be a main sequence star or a more evolved subgiant star. It is around 132 million years old and is spinning rapidly with a projected rotational velocity of 296.8 km/s. This is giving the star an oblate shape, with an estimated equatorial girth that is 30% larger than the polar radius. The star has an estimated 2.3 times the mass of the Sun and 2.7 times the Sun's radius.
Upsilon2 Centauri is a binary star system in the southern constellation Centaurus. Its name is a Bayer designation that is Latinized from υ2 Centauri, and abbreviated Upsilon2 Cen or υ2 Cen. This system is visible to the naked eye as a point of light with a combined apparent visual magnitude of +4.33. Based upon an annual parallax shift of 2.57 mas as seen from Earth, this star is located roughly 1,300 light years from the Sun. Relative to its neighbors, the system has a peculiar velocity of 39.2+8.8−15.2 km/s and it may form a runaway star system. This is a single-lined spectroscopic binary star system with an orbital period of 207.357 days and an eccentricity of 0.55. The primary component has the spectrum of an evolved F-type giant/bright giant hybrid with a stellar classification of F7 II/III. It is around 46 million years old with 6.9 times the mass of the Sun. The star is radiating 3,919 times the Sun's luminosity from its photosphere at an effective temperature of 6,495 K.
Sigma Centauri is a solitary star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from σ Centauri, and abbreviated Sigma Cen or σ Cen. This star is visible to the naked eye with an apparent visual magnitude of 3.91. A visual companion at an angular separation of 88.11±0.37 mas along a position angle of 14.33°±2.59° was detected in 2010 using interferometry, but its association with Sigma Centauri remains undetermined as of 2013. The distance to Sigma Centauri, based upon an annual parallax shift of 7.92 mas, is around 412 light years. This is a B-type main sequence star with a stellar classification of B3 V. It is a helium-rich star, the most massive type of chemically peculiar star. Sigma Centauri has around 6.8 times the mass of the Sun and 4.5 times the Sun's radius. It has a relatively high rate of spin with a projected rotational velocity of 169 km/s, and is around 25 million years old. The star radiates 1,101 times the solar luminosity from its outer atmosphere at an effective temperature of 15,744 K. It is a member of the Lower Centaurus Crux component of the Scorpius–Centaurus association.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
