{{short description|Binary star in the constellation Draco}} {{Starbox begin}} {{Starbox image | image=[[File:HPDra TESS data.png|280px]] |caption=[[Light curve]] for HP Draconis, plotted from [[Transiting Exoplanet Survey Satellite|TESS]] data.<ref name=TESS/> }} {{Starbox observe | epoch = J2000 | constell = [[Draco (constellation)|Draco]]<ref name=XHIP/> | ra = {{RA|18|54|53.4810}}<ref name=DR3/> | dec = {{DEC|+51|18|29.792}}<ref name=DR3/> | appmag_v = 7.974<ref name=milone2010/><br>(8.234 <small>(primary eclipse)</small>, 8.204 <small>(secondary eclipse)</small>)<ref name=milone2010/> }} {{Starbox character | type = [[Main sequence]] + [[main sequence]]<ref name=milone2010/> | class = F9V + F9V<ref name=XHIP/> | u-b = | b-v = | variable = [[Eclipsing binary]]<ref name=Southworth2025/> }} {{Starbox astrometry | radial_v = {{Val|-16.07|0.63}}<ref name=Milone2005/> | prop_mo_ra = +23.234 | prop_mo_dec = +83.306 | pm_footnote = <ref name=DR3/> | parallax = 12.6153 | p_error = 0.0516 | parallax_footnote = <ref name=DR3/> | absmag_v = {{Val|3.46|0.08}}<ref name=milone2010/> }} {{Starbox orbit | reference = <ref name=Southworth2025/> | period_unitless = {{val|10.76154|0.00009}}<ref name=Milone2005/> days | axis_unitless = {{Val|26.814|0.017|ul=solar radius}} | eccentricity = {{Val|0.03647|0.00011}} | inclination = {{Val|87.5554|0.0060}} | periarg_primary = {{Val|41.38|0.19}} | k1 = {{val|61.971|0.056}} | k2 = {{Val|64.067|0.060}} }} {{Starbox detail | source = <ref name=Southworth2025/> | component1 = HP Draconis A | mass = {{Val|1.1354|0.0023}} | radius = {{Val|1.2474|0.0046}} | luminosity = {{Val|1.82|0.19|0.17}} | temperature = {{Val|6000|150|fmt=commas}} | gravity = {{val|4.3012|0.0032}} | rotational_velocity = {{Val|5.864|0.021}} | metal_fe = | age_gyr = 3.5 | component2 = HP Draconis B | mass2 = {{Val|1.0984|0.0022}} | radius2 = {{Val|1.1498|0.0049}} | luminosity2 = {{Val|1.48|0.12|0.11}} | temperature2 = {{Val|5935|150|fmt=commas}} | gravity2 = {{val|4.3376|0.0037}} | rotational_velocity2 = {{Val|5.406|0.023}} | metal2_fe = | age_gyr2 = 3.5 }} {{Starbox catalog | names = {{odlist |HD=175900 | HIP=92835 | BD=+51°2459 | TYC=3552-394-1 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad=HP+Dra }} {{Starbox end}} '''HP Draconis''' is a [[binary star]] system in the constellation of [[Draco (constellation)|Draco]]. At an [[apparent magnitude]] of +7.974, it is not visible to the [[naked eye]]. [[stellar parallax|Parallax]] measurements give a distance of {{convert|259|ly|pc|abbr=off|lk=on}}.
==Characteristics== This is an [[eclipsing binary]] system whose components are [[detached binary|detached]].<ref name=Southworth2025/> Each 10.76 days (the orbital period of the system),<ref name=vsx/> the apparent magnitude of the system drops to 0.26 in the primary (deeper) eclipse and to 0.23 in the secondary eclipse.<ref name=milone2010/> The variability of this system was discovered in 1997 by the [[Hipparcos]] satellite, and it was given its [[variable-star designation]] ''HP Draconis'' in 1999.<ref name=Southworth2025/>
The components of this binary system are separated by {{convert|26.814|solar radius|km au}} with an [[orbital eccentricity|eccentricity]] of 0.036.<ref name=Southworth2025/> Both are [[F-type main-sequence star]]s with identical [[stellar classification]]s of F9V.<ref name=XHIP/> Star A has 1.135 times the [[solar mass|mass]], 1.247 times the [[radius of the Sun|radius]], and 1.8 times the [[luminosity of the Sun]], while star B has 1.098 times the mass, 1.15 times the radius, and 1.48 times the Sun's luminosity. The [[effective temperature]]s are 6,000 and {{Val|5935|ul=K|fmt=commas}},<ref name=Southworth2025/> giving them the yellow-white hue typical of [[late-type star|late-type]] [[F-type star]]s.<ref name=csiro/> The estimated age of the system is 3.5 billion years. There is evidence of a third component in the system from eclipse timing variations.<ref name=Southworth2025/>
HP Draconis makes a wide triple system with a [[white dwarf]] that has a [[projected separation]] of 1,140 [[astronomical unit]]s, giving an estimated orbital period of 23,000 years. This companion has 0.45 times the Sun's mass, a temperature of {{Val|7087|205|fmt=commas|u=K}} and has been a white dwarf for an estimated 1.15 billion years.<ref name=Jalowiczor2021/>
==References== <references>
<ref name=XHIP>{{Cite XHIP|92835}}</ref>
<ref name=SIMBAD>{{Cite SIMBAD|title=HP Dra}}</ref>
<ref name=DR3>{{Cite DR3|2144465183642116864}}</ref>
<ref name=milone2010>{{cite journal |last1=Milone |first1=E. F. |last2=Kurpińska-Winiarska |first2=M. |last3=Oblak |first3=E. |title=Observations and Analyses of the Eccentric Orbit Eclipsing Binary HP Draconis |journal=The Astronomical Journal |date=2010 |volume=140 |issue=1 |page=129 |doi=10.1088/0004-6256/140/1/129 |bibcode=2010AJ....140..129M }}</ref>
<ref name=Southworth2025>{{cite journal |last=Southworth |first=John |title=Rediscussion of eclipsing binaries. Paper XXVI. The F-type long-period system HP Draconis |date=2025-08-06 |arxiv=2508.04218 |journal=The Observatory}}</ref>
<ref name=Jalowiczor2021>{{Cite journal |last1=Jalowiczor |first1=Peter A. |last2=Casewell |first2=Sarah |last3=Schneider |first3=Adam C. |last4=Faherty |first4=Jacqueline K. |last5=Kuchner |first5=Marc J. |date=2021-07-22 |title=Identification of a White Dwarf Companion in the V* HP Dra System |journal=Research Notes of the AAS |volume=5 |issue=7 |pages=170 |doi=10.3847/2515-5172/ac151f |bibcode=2021RNAAS...5..170J |doi-access=free |issn=2515-5172}}</ref>
<ref name=vsx>{{Cite web |title=VSX : Detail for HP Dra |url=https://vsx.aavso.org/index.php?view=detail.top&oid=13888 |access-date=2025-08-08 |website=vsx.aavso.org}}</ref>
<ref name=TESS>{{cite web |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=1 August 2025}}</ref>
<ref name=Milone2005>{{Cite journal |last1=Milone |first1=E. F. |last2=Munari |first2=U. |last3=Marrese |first3=P. M. |last4=Williams |first4=M. D. |last5=Zwitter |first5=T. |last6=Kallrath |first6=J. |last7=Tomov |first7=T. |date=2005-10-01 |title=Evaluating Gaia performances on eclipsing binaries - IV. Orbits and stellar parameters for SV Cam, BS Dra and HP Dra |journal=Astronomy & Astrophysics |language=en |volume=441 |issue=2 |pages=605–613 |doi=10.1051/0004-6361:20052734 |arxiv=astro-ph/0506106 |bibcode=2005A&A...441..605M |issn=0004-6361}}</ref>
<ref name=csiro>{{cite web | title=The Colour of Stars | date=December 21, 2004 | work=Australia Telescope, Outreach and Education | publisher=Commonwealth Scientific and Industrial Research Organisation | url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html | accessdate=2012-01-16 | archive-date=2013-12-03 | archive-url=https://web.archive.org/web/20131203222826/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html | url-status=dead }}</ref>
</references> {{sky|18|54|53.48|+|51|18|29.8|259}} {{Stars of Draco}} [[Category:Draco (constellation)]] [[Category:F-type main-sequence stars]] [[Category:Objects with variable star designations|Draconis, HP]] [[Category:Durchmusterung objects|BD+51 2459]] [[Category:Hipparcos objects|175900]] [[Category:Henry Draper Catalogue objects|092835]]